Pygrib

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* remove python 3.6 support, add python 3.11,3.12
* add __dir__ method so dir(grb) returns grib keys.
* allow pygrib.open to open a path specified by a PathLike object
* fix compilation issues on macos x
* allow pygrib.open to take an io.BufferedReader object as an argument
(issue 83, PR 206)
* ensure that RuntimeError contains a message of type `str` (PR 212)
* fix an issue that the 3rd bit of scanning mode does not affect processing (PR 213)

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* move conftest.py to test dir (so tests can be run from there)
* add check-manifest test to github actions workflow.
* update some cartopy test scripts to remove deprecation warnings.
* move package under 'src' dir so import pygrib works in install dir.
* add windows and macos x tests.
* make sure gribmessage.__repr__ doesn't fail is shapeOfTheEarth parameter
is missing (issue 177).
* move private eccodes dir inside 'share', so `import eccodes` doesn't import an empty package.

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* fix pygrib.get_definitions_path() so it works if set_definitions_path has not been called.
* add conftest.py to MANIFEST.in (issue 171)

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* use pytest-mpl for image comparison tests.
* change license to MIT.
* changes gribmessage.projparams['proj'] from 'cyl' to 'longlat'
for non-projection projections (e.g. 'regular_ll'). Issue 167.
* reorganize to include eccodes definitions inside package
when wheels are build (PYGRIB_WHEEL env var is set).
Add set_definitions_path/get_defintions_path module functions
to get/reset ECCODES_DEFINITION_PATH.
* include binary wheels for linux in pypi release.
* add grid template definition for RAP grib files in binary wheels (issue 134).
Not fully implemented, but at least file can be read (gridType=unknown, latlons
method doesn't yet work)..

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* clean up docs.
* migrate examples in 'test' directory from basemap to cartopy.
* enable github actions for CI (PR 159).

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* split ncepgrib2 module into a separate project
(https://github.com/jswhit/ncepgrib2). pygrib now only uses
eccodes. Docs converted to sphinx.