Icclim

This 5.2.1 release supersedes 5.2.0 which had unpolished finishes.
As usual the package is available on [pypi](https://pypi.org/project/icclim/) and [conda-forge](https://anaconda.org/conda-forge/icclim).

Breaking changes
None

Bug fixes
`slice_mode` seasonal samplings was giving wrong results for quite a few indices. This has been fixed and the performances should also be improved by the fix.
However, now seasonal slice_mode does not allow to use xclim missing values mechanisms.
user_index ExtremeMode config was not properly parsed when a string was used.
user_index Anomaly operator was not properly using the `ref_time_range` to setup a reference period as it should.
user_index Sum and Mean operators were broken due to a previous refactoring and a lack of unit tests, it is now fixed and tested.
`create_optimized_zarr_store` would throw an error when creating the first temp store if the chunks were not unified.

Internal changes
Made Frequency part of SliceMode union.
Changed how `rechunker` dependency is pinned to add flexibility. We want a version above '0.3' but not the '0.4'.
For the newly generate API, on `custom_index` function, the parameter `user_index` is now mandatory.
Update release process.

Enhancements
Improve `create_optimized_zarr_store` to accept a chunking schema instead of a single dim.
Make use of `fsspec` to generalize the storages where `create_optimized_zarr_store` can create its zarr stores.
Make CSDI and WSDI threshold configurable using the `threshold` parameter of icclim.index.
Add a function in `icclim` namespace for each ECA&D index for convenience.
Improved documentation about chunking.
Improved dev documentation display on readthedocs.

Breaking changes
- Parameter `out_file` default value is now None. When it is None, `icclim.index` does not write the output on a netCDF.
- Minimal required xclim version is now 0.34
- Pinned dask dependency: `dask<2022.01.1` for rechunker 0.3.3 to work.

API changes
- Added `icclim.indices` to compute multiple indices at once.
- Added experimental feature `icclim.create_optimized_zarr_store`. It is a context manager which can be used to rechunk a dataset using without any chunk on the specified dimension. It makes use of `rechunker`[0] library.

Bug fixes
- Fixed WSDI and CSDI. They were computing percentiles on the wrong period.
- Fixed WW, WD, CW, CD. Their binding with xclim was not properly made and was throwing an error.
- Fixed setup.py dependency to the whole world. This make installation from sources possible in a clean environment.

Maintenance
- Improved icclim CI (code coverage)
- Improved code quality (unit test, refactoring)
- Added contribution guide
- Improve overall typing

[0] https://github.com/pangeo-data/rechunker/

Official release of icclim 5.0.2 (a.k.a icclim v5)
For full details of the changes see https://icclim.readthedocs.io/en/latest/references/release_notes.html

In short, icclim has be rewritten to make use of xclim, xarray and dask libraries.
The scope is unchanged, icclim still computes 49 ECA&D climate indices and provides an API to create custom indices.

icclim 5.0.2 is available on both pip and conda-forge.

Fixed new setup.py so that it includes correctly data files, including .so files.
First tests also for python 2.7+ support (updated setup.py).

Has been tested only with python 3.6 (anaconda).
Requires netCDF4-python 1.3.0 pre-release (not (yet) compatible with python 2.x).
Final release will work on both python 2.7+ and 3.4+.

Removed utime since cftime to not support anymore this deprecated function.