Changes
- move work-in-progress modules to module branches (389)
- rename `skypy.galaxy` to `skypy.galaxies` (413)
- move `galaxy.size` and `galaxy.ellipticity` to `galaxy.morphology` (410)
- refactored kcorrect spectrum functions (379, 386, 391)
- obtain metallicity and star formation rates from templates (397, 400)
- new `utils.photometry` module (411)
- use speclite package for magnitude computations (292, 368)
- improved examples (385, 388, 395)
- refactored Schechter stellar mass sampling (394)
- random projection of triaxial ellipsoid (407)
- change `fsky` to `sky_area` (314)
- simple construction of quantities in config files (316)
- drop support for astropy 3 (353)