Implement std::hash for Str::StringRef
Add framework/Resource and use it for audio/Sample

This is somewhat WIP, there are a few blocking TODOs,
especially the one near the declaration of Manger::Register
Add the S_{Begin/End}Registration syscalls and use them in cgame
Resource: introduce a Handle WIP for c&c
Fix compilation of std::hash<Str::StringRef>
Fix a stupid 'optimization' in std::hash<Str::StringRef>
Update the doc of Resources for Handles
Merge branch 'master' into engine-upgrade/sound_resources
Fix the TTY client build
Resource: improvements to Resource made when trying to use it in the renderer
Merge branch 'engine-upgrade/sound_resources'