color themes. (EXPERIMENTAL)

CMake: Require C++20 support in compiler

Closes #96

See merge request rncbc/qpwgraph!11

  to Patchbay > Auto Disconnect option. (qpwgraph issue #93) (EXPERIMENTAL)

  to disable the ALSA MIDI/Sequencer graph conveniency in a whim.
  (EXPERIMENTAL)

  node and reusing a previous port id. (EXPERIMENTAL)

  patchbay is deactivated and auto-pin is off. (GL issue #93)

Added author credits

See merge request rncbc/qpwgraph!10

Added some basic user manual

See merge request rncbc/qpwgraph!9

As simple and as intuitive as qpwgraph can be, a proper documentation is
more than welcome.

For instance, I didn't know about  the INSERT/DELETE shorcuts until I
read the ChangeLog; and I didn't know about the Ctrl/Shift modifiers for
rectangular selection until I read a random comment on some issue on
GitLab.

  short lived nodes, recycled by reusing the very same ids... (3)

  short lived nodes, recycled by reusing the very same ids... (2)

  short lived nodes, recycled by reusing the very same ids...

  lived nodes, recycled by reusing the very same ids. (EXPERIMENTAL)
- Cope with nodes that can possibly remain with the very same name
  but different ids. (GL #91) (EXPERIMENTAL)

- Attempt to cope with nodes that can possibly remaining with very same name but different ids. (hopefully fixes issue #91)

  (-n, --nonexclusive) command line options. (GH #27) (EXPERIMENTAL)