* reworked some resource loading and mod init stuff
* texetures are now configured at runtime via .toml files
* moved from SRF to messagepack
* changed folder structures
* added the fmt library (for later)

I haven't actually written any tests yet, but now I can at least
easily write tests when I want to. Also, just having one
.t.cc file for each header means we get to test each header
in isolation, to prevent include order issues.