Pysatmissions

* Add support for skyfield propagation
* Maintenance
* Update pytest syntax
* Update Github Actions versions
* Add manual GitHub Actions tests for pysat RC
* Add manual GitHub Actions tests for optional dependencies
* Add manual GitHub Actions tests for pysatMissions RC
* Remove optional dependencies in readthedocs requirements
* Add tests for NEP 29 testing
* Add tests for Mac OS
* Deprecate `calculate_ecef_velocity` method
* Use pyproject.toml to handle metadata / installation
* Update GitHub Actions workflow standards
* Testing
* Include checks on sc coordinate transformation calculations

* Documentation Updates

* Make fortran dependencies optional installs
* aacgmv2
* apexpy
* OMMBV
* Access logger directly from pysat
* Use pysat deprecation tests
* Incorporate Windows tests into Github Actions
* Bug Fix
* Ensure default num_samples consistent for one day regardless of cadence
* Maintenance
* Update instrument test standards
* Added `utils.package_check`, a standard decorator to bypass functions using
packages that are optional installs if the package is not installed
* Use local vector functions rather than import from OMMBV

* Include license in package manifest

* Add Keplerian orbital inputs into missions_sgp4
* Update sgp4 interface to use new syntax for initialization from TLEs
* Include conversions to geodetic latitude / longitude / altitude for sgp4
* Improve metadata generation in missions_sgp4
* Update syntax to be compliant with OMMBV 1.0
* Documentation
* Improve docstrings throughout
* Added bypass for apexpy for readthedocs build
* Deprecations
* Deprecated missions_ephem, as pyephem will no longer be updated
* Testing
* Add style check for docstrings
* Added checks for deprecation warnings
* Improve checks in codeclimate

* Migrate pyglow interface to pysatIncubator
* Style updates for consistency with pysat 3.0
* Use `inst_id` instead of `sat_id`
* Use `cadence` instead of `freq`
* Use 'missions' as the platform name ('pysat' now reserved for core code)
* Migrate CI testing to Github Actions
* Use OMMBV instead of pysatMagVect