Add docs/api to .gitignore
Fix sphinx warning for ElectronOZM docstring
Add missing __all__ to onezone.py
Remove corner import from plot.py (fixes sphinx docs warning)
Remove redundant file docs/gammafit/index.rst (fixes sphinx warning)
Restructure Sphinx docs a bit
Add `intersphinx_mapping` entries to Sphinx configuration file
Add package docstring.

(I might have removed that one accidentally before)