Ouranosinc/xclim: v0.23.0

Breaking changes Renamed indicator atmos.degree_days_depassment_date to atmos.degree_days_exceedance_date. In degree_days_exceedance_date : renamed argument start_date to after_date. Added cfchecks for Pr+Tas-based indicators. Refactored test suite to now be available as part of the standard library installation (xclim.testing.tests). Running pytest with xdoctest now requires the rootdir to point at tests location (pytest --rootdir xclim/testing/tests/ --xdoctest xclim). Development checks now require working jupyter notebooks (assessed via the pytest --nbval command). New indicators rain_approximation and snowfall_approximation for computing prlp and prsn from pr and tas (or tasmin or tasmax) according to some threshold and method. solid_precip_accumulation and liquid_precip_accumulation now accept a thresh parameter to control the binary snow/rain temperature threshold. first_snowfall and last_snowfall to compute the date of first/last snowfall exceeding a threshold in a period. New features and enhancements New kind entry in the parameters property of indicators, differentiating between [optional] variables and parameters. The git pre-commit hooks (pre-commit run --all) now clean the jupyter notebooks with nbstripout call. Bug fixes Fixed a bug in indices.run_length.lazy_indexing that occurred with 1D coords and 0D indexes when using the dask backend. Fixed a bug with default frequency handling affecting fit indicator. Set missing method to 'skip' for freq_analysis indicator. Fixed a bug in ensembles._ens_align_datasets that occurred when inputs are .nc filepaths but files lack a time dimension. Internal changes core.cfchecks.check_valid now accepts a sequence of strings as its expected argument. Clean up in the tests to speed up testing. Addition of a marker to include "slow" tests when desired (-m slow). Fixes in the tests to support sklearn>=0.24, clisops>=0.5 and build xarray@master against python 3.7. Moved the testing suite to within xclim and simplified tox to manage its own tempdir. Indicator class now has a default_freq method