[GSoC'21 Weekly Update #5] Sound mixer improvements

[Christos Margiolis]

Hello,

This is last week's report:

Kernel:

- The volume-read ioctl reported the actual volume of the device, which 
  means that if a device is muted, it'd report a volume of 0. I changed 
  that so that when a device is muted, it reports the muted volume
  instead of the actual one. This is especially useful in userland
  programs.
- Modified the volume-set ioctl so that the volume can be changed even
  when a device is muted.
- Got the code up for review on Phabricator: 
  https://reviews.freebsd.org/D31130

mixer(3):

- Experimented with different volume handling designs.
- Cleaned up and simplified the main structures; removed useless flags,
  struct fields and code.

mixer(8):

- Mostly code refactoring.

The code is available on:
- GitHub: https://github.com/christosmarg/mixer
- Sourcehut: https://git.sr.ht/~crm/mixer
- My Git server: https://git.margiolis.net/mixer/files.html

The project's Wiki article can be found at: 
- https://wiki.freebsd.org/SummerOfCode2021Projects/SoundMixerImprovements