v2.1.9

Summary:
Started adding more functions to eventually add solve capability via the response method. Exposed parameters for setting the buffer distance when cropping tide model data (thanks @robbibt!). Fixed the TMD3 netCDF4 variables for currents (thanks @VikNikolaus!). Improved the CI builds by having test files versus a side-by-side comparison against the matlab version, which allowed the addition of windows builds. Added some improvements to the documentation, including the use of bibtex for citations.

Itemized Changes:

• feat: add spherical harmonic functions (#362)
• refactor: move generic astro functions to math.py (#362)
• feat: add function to calculate altitude, azimuth and D (#362)
• test: add test for unnormalized legendre polynomials (#362)
• test: moved normalize_angle test to test_math.py (#362)
• test: add ECEF to altaz test at USNO (#362)
• feat: add calculation of zenith angle (#363)
• test: add zenith angle test (#363)
• feat: expose buffer distance to crop tide model data for #367 (#368)
• test: add constituent parameter test (#368)
• ci: add windows build for #98 (#369)
• fix: omega and phase in constituent parameters (#369)
• refactor: move body tide Love/Shida numbers to arguments (#369)
• test: create test files from matlab program for comparison (#369)
• fix: add missing_ok to deletions in tests (#369)
• fix: verify that file objects are closed in test_spatial (#369)
• fix: latest TMD3 current variable names for #370 (#371)
• feat: add tidal aliasing period calculation function (#371)
• fix: add latitude and longitude as potential dimension names (#371)
• docs: use sphinxcontrib-bibtex to build bibliography (#372)
• refactor: moved check points function to compute (#372)
• docs: unify all references to a single page (#372)
• docs: rearrange toctrees

Full Changelog: 2.1.8...2.1.9