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
Build unified client with rendererGL.
Remove old renderer files.
Lots of configuration migration script fixes. New dirs in /etc.
Fix dir cleanup (broke the debian/rules ‘clean’ target).

This fixes commit fc3af440da27e3aa185b7c30863165208a0189ac.
Update unvanquished-server news file.
Merge branch 'master' into debian
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 'master' into debian; update changelog
Modify basepak.sh to handle pk3 names and versioning; fix empty-string tests.
Clang-specific warning is already covered by -Wpedantic
Don't allow clients to connect to a server that uses pk3dirs