Only read body if it's Gemtext

I *think* this saves a bunch of bandwidth and speeds things up.
Remove pointless returns
Fix incorrect type in Sprintf call
Handle (somewhat) all possible Gemini response codes
Ignore new binary name
Add a basic, hacky, implementation

This also renames to gemlint (since just crawling isn't sufficient),
and removes cobra because we don't need the extra complexity right
Add Gemini library
Centralise Copyright and licensing in the README
Import WTFNMFPL licensed skeleton