bbfrederick/rapidtide: Version 2.0alpha15 - 3/17/21 checkpoint release

(rapidtide) Added a new method for generating global signal using PCA. (all) Further imports from master branch to improve deployment. (simdata) Complete overhaul - new parser better checks, more flexible input formats. (io.py) Improvements to readvecs to handle very large files. (ccorrica, filttc, histtc, pixelcomp, resamp1tc) Facelift, cleanup, new parsers. (testing) Removed python 2.7 CI build. (all) Addressed many linter issues, updated deprecated numpy and scipy calls