Add support for Fossil and Mercurial

[nobodywasishere]

This may require minor refactoring, but all we need to figure out to use these tools is:

• check if a given url is a valid repository of that vcs type
• get a list of all the tags and their hashes without cloning
• get the name and hash of the main branch without cloning
• cloning the repository
• forcefully checking out a specific tag

How repos are parsed will also have to be changed, as the largest fossil host doesn't follow the domain.tld/user/proj format.

The current git functionality all lives entirely within CrystalDoc::VCS

Example Crystal Fossil repo for testing:
https://chiselapp.com/user/MistressRemilia/repository/remiaudio/index

If anyone knows of an example mercurial one please let me know!

[nobodywasishere]

Added a fossil builder in 52ae389, still need to add support for querying for new versions and submitting new fossil repos

[nobodywasishere]

Manually added this to the database:

https://crystaldoc.info/chiselapp/MistressRemilia/libremiliacr/v0.11.2/index.html