Some major refactors in spherical harmonic dependencies
Added new SMB programs and new capabilities
* `feat`: add GSFC GIA program (35)
* `feat`: shift ERA P-E, MERRA-2 SMB and GLDAS TWS to mid-month values (35)
* `feat`: add option `--mask` to GLDAS harmonics to use custom (35)
* `feat`: added flatten option to MERRA-2 subsetter (38)
* `feat`: add downscaled RACMO harmonic program (39)
* `feat`: add MERRA2-hybrid v1.2.1 (40)
* `feat`: add JPL-GEMB SMB harmonic programs (41)
* `feat`: add `constants` class with ellipsoidal and gravity parameters (45)
* `refactor`: MERRA hybrid variable defaults to include firn height to address 31 (32)
* `refactor`: use f-strings for formatting ascii and verbose output (42)
* `refactor`: single implicit import of spherical harmonic tools (44)
* `refactor`: function for associated legendre polynomials (46)
* `fix`: slimmer build for documentation (33)
* `fix`: hardcode GSFC subsetting api url (36)
* `fix`: adjust time range for CMR queries (36)
* `fix`: JPL ECCO sync for LLC tiles (37)
* `fix`: racmo downscaled regex pattern
* `fix`: added function to attempt to get variable attributes (43)
* `fix`: copy input date variables to output spatial object (43)
* `fix`: don't add `get_git_revision_hash` to files
* `fix`: regex string prefix in reanalysis (46)
* `docs`: add descriptors about NASA cloud migration for PODAAC and GESDISC (32)
* `docs`: updated structure of documentation (34)
* `docs`: use `sphinx-argparse` `v0.4.0` (42)
**Full Changelog**: https://github.com/tsutterley/model-harmonics/compare/1.0.0.3...1.1.0