qt: don't define std::hash<QString> for qt >= 5.14

the hashes were defined in qtbase.git 4469e36d7203a55a4e158a50f0e9effc3f2fa3c2.

renderer: use shared_ptrs for renderer resources

SMP damage modifier

Better wording leads to better understanding (hopefully)..

- "bundle" changed to "frame"
- "frame" changed to "layer"

Add "mod snapshots" idea to docs

Revised slp-files.md

I revised the documentation merging it with my own notes and documentation. I had quite a bit of information to add, so the documentation took a bit of an overhaul.

SMX file support

Fix crash because of missing null-initialization of pointer

Fixes #1197 and #1190 I think

First batch of clang-tidy fixes

included review changes

Minimise state changes in renderer

CI: Removing Travis, adding Github Workflow for MacOSX

adding Github Workflow for MacOSX

CI: Changed travis.yml to internal package management

clone depth set to 1

Spelling

The FindOpusfile module wrongfully assumed that opus.h and opusfile.h
are always in the same directory. If one header was installed manually
or the user has a functional package manager, this is not true.

The third directory is for opusfile.h, which includes
<opus_multistream.h>.