Rename project to repod

Rename the project to repod.

This cleans up a lot of code mentions and additionally:

• moves the default config and config override location to a more logical location (switching to a .conf file suffix)
• replaces all top-level .rst files with .md files, while simplifying README and extending CONTRIBUTING
• adds license statement for user facing documentation (GFDL1.3-or-later)

Fixes #45 (closed)