borglab/gtsam: Release 4.2a9

This is hopefully the last 4.2 pre-release. I had planned to cut 4.2 this weekend but there were still apparently some issues with the wrapper when used in Georgia tech's CS 3630 course (325 students using GTSAM) and so I'd rather wait another week for these things to settle down. In the meantime, though, we needed a pre-release so %pip install gtbook works on Google Colab and installs 4.2a9 in the process. All works now, as evidenced at roboticsbook.org. The biggest changes are: moved away from boost utilities to c++ initializers in all tests and examples. a cleaned up and correctly working hybrid inference framework. Thanks @varunagrawal and @ProfFan ! template-magical NoiseModelFactorN which allows an arbitrary number of variables connected to factors. Thanks @gchenfc ! several important bug-fixes and edits, by many new contributors, listed below: New Contributors @nkhedekar made their first contribution in https://github.com/borglab/gtsam/pull/1330 @MigVega made their first contribution in https://github.com/borglab/gtsam/pull/1331 @ulterzlw made their first contribution in https://github.com/borglab/gtsam/pull/1340 @jrpowers made their first contribution in https://github.com/borglab/gtsam/pull/1361 @stefangachter made their first contribution in https://github.com/borglab/gtsam/pull/1296 @njayakumar3 made their first contribution in https://github.com/borglab/gtsam/pull/789 @BrettRD made their first contribution in https://github.com/borglab/gtsam/pull/1376 @acowley made their first contribution in https://github.com/borglab/gtsam/pull/1381 Detailed Changes Add an expression for normalize() by @nkhedekar in https://github.com/borglab/gtsam/pull/1330 Update README.md by @MigVega in https://github.com/borglab/gtsam/pull/1331 Hybrid Elimination by @varunagrawal in https://github.com/borglab/gtsam/pull/1339 Fixed Jacobian in python CustomFactorExample by @ulterzlw in https://github.com/borglab/gtsam/pull/1340 Hybrid Mixture Error by @varunagrawal in https://github.com/borglab/gtsam/pull/1318 Hybrid Multifrontal by @varunagrawal in https://github.com/borglab/gtsam/pull/1323 NoiseModelFactorN - fixed-number of variables >6 by @gchenfc in https://github.com/borglab/gtsam/pull/947 GaussianConditional logDeterminant by @varunagrawal in https://github.com/borglab/gtsam/pull/1345 Replace NoiseModelFactor1 in with NoiseModelFactorN in pre-made factors by @gchenfc in https://github.com/borglab/gtsam/pull/1344 Hybrid Bayes Net sampling by @varunagrawal in https://github.com/borglab/gtsam/pull/1347 Fix wrapper warnings by @varunagrawal in https://github.com/borglab/gtsam/pull/1348 Update geometry.i : wrap multiplication of Rot3 and Unit3 by @akshay-krishnan in https://github.com/borglab/gtsam/pull/1302 Sampling test for Hybrid Posterior by @varunagrawal in https://github.com/borglab/gtsam/pull/1346 Some refactoring and new test by @dellaert in https://github.com/borglab/gtsam/pull/1349 Add logDensity and evaluate to GaussianBN and HybridBN by @dellaert in https://github.com/borglab/gtsam/pull/1352 Added convenience constructors and python wrappers by @dellaert in https://github.com/borglab/gtsam/pull/1353 Wrap constructors for PreintegratedAhrsMeasurements by @varunagrawal in https://github.com/borglab/gtsam/pull/1354 HybridValues specify continuous then discrete by @varunagrawal in https://github.com/borglab/gtsam/pull/1355 Likelihoods and other improvements by @dellaert in https://github.com/borglab/gtsam/pull/1356 Proper Hybrid Elimination by @varunagrawal in https://github.com/borglab/gtsam/pull/1319 Test on ratio by @dellaert in https://github.com/borglab/gtsam/pull/1357 Hybrid Improvements by @varunagrawal in https://github.com/borglab/gtsam/pull/1343 Fix HybridGaussianFactorGraph error by @varunagrawal in https://github.com/borglab/gtsam/pull/1358 Initializer list and insert/update chaining by @dellaert in https://github.com/borglab/gtsam/pull/1359 Slightly expand Python API by @jrpowers in https://github.com/borglab/gtsam/pull/1361 Check for native architecture and set GTSAM_COMPILE_OPTIONS_PUBLIC accordingly by @stefangachter in https://github.com/borglab/gtsam/pull/1296 Fix hybrid tests by @varunagrawal in https://github.com/borglab/gtsam/pull/1363 Fixed a few small issues... by @dellaert in https://github.com/borglab/gtsam/pull/1367 Switch to EliminateDiscrete for max-product by @dellaert in https://github.com/borglab/gtsam/pull/1362 Hybrid Serialization by @varunagrawal in https://github.com/borglab/gtsam/pull/1368 Various fixes for Hybrid by @varunagrawal in https://github.com/borglab/gtsam/pull/1369 Hybrid Elimination with Normalization Constant by @varunagrawal in https://github.com/borglab/gtsam/pull/1360 Added *.bib file and started adding citations to README.md by @njayakumar3 in https://github.com/borglab/gtsam/pull/789 Un-deprecate NoiseModelFactor1-6 and move X1 and key1-6 shortcuts to NoiseModelFactorN by @gchenfc in https://github.com/borglab/gtsam/pull/1370 Two new tests, one with 5 modes by @dellaert in https://github.com/borglab/gtsam/pull/1371 Simplified AP for HybridBayesNet by @dellaert in https://github.com/borglab/gtsam/pull/1372 DefaultOrderingFunc in EliminationTraits by @varunagrawal in https://github.com/borglab/gtsam/pull/1373 Big Re-"Factor" of Hybrid by @dellaert in https://github.com/borglab/gtsam/pull/1374 More Expression wrappers by @BrettRD in https://github.com/borglab/gtsam/pull/1376 Get rid of boost::assign by @dellaert in https://github.com/borglab/gtsam/pull/1375 replace list_of with initializer list in TimeTBB.cpp by @kartikarcot in https://github.com/borglab/gtsam/pull/1379 Harmonized error/logProbability in entire Factor/Conditional hierarchy by @dellaert in https://github.com/borglab/gtsam/pull/1380 BatchFixedLagSmoother: add ability to limit warning debug prints by @acowley in https://github.com/borglab/gtsam/pull/1381 Test and fix all conditionals by @dellaert in https://github.com/borglab/gtsam/pull/1386 Some Hybrid Improvements by @varunagrawal in https://github.com/borglab/gtsam/pull/1387 Hybrid/simplify by @dellaert in https://github.com/borglab/gtsam/pull/1388 Correction to docs and lambdas by @varunagrawal in https://github.com/borglab/gtsam/pull/1390 Switch pruning test to probabilities. by @dellaert in https://github.com/borglab/gtsam/pull/1394 Deprecate filter by @dellaert in https://github.com/borglab/gtsam/pull/1397 Fix examples that were using filter by @dellaert in https://github.com/borglab/gtsam/pull/1402 Deprecated boost transform_iterators by @dellaert in https://github.com/borglab/gtsam/pull/1407 Iterator for 4.2 by @dellaert in https://github.com/borglab/gtsam/pull/1417 Fix (issue #1336) dangling pointer access violation. by @oicchris in https://github.com/borglab/gtsam/pull/1423 Fix version... by @dellaert in https://github.com/borglab/gtsam/pull/1424 4.2 fixes by @varunagrawal in https://github.com/borglab/gtsam/pull/1425 Patch ros package (branch: release/4.2) by @jlblancoc in https://github.com/borglab/gtsam/pull/1427 Add missing header to fix gtbook by @dellaert in https://github.com/borglab/gtsam/pull/1429 Full Changelog: https://github.com/borglab/gtsam/compare/4.2a8...4.2a