feat: add movemouse-smooth-diagonals

[rszyma]

Describe your changes. Use imperative present tense.

Closes #549

Add movemouse-smooth-diagonals cfg option that enables smooth diagonal movements by storing a previous movemouse action in a 1-length buffer. If the next movemouse has different axis than the one in the buffer both actions are outputted at the same time.

A few remarks:

• So far I've only did implementation for Linux (I haven't tried implementing win nor wintercept yet).
• This cfg option is intended to work only with movemouse actions that have the same interval, otherwise the behavior is undefined.
• Using this cfg option adds a delay to movemouse actions equal to the interval of used movemouse actions.

Checklist

• Add documentation to docs/config.adoc
  • Yes
• Add example and basic docs to cfg_samples/kanata.kbd
  • Yes
• Update error messages
  • N/A
• Added tests, or did manual testing
  • Manual testing

[jtroo]

Tried fixing merge conflicts through the GitHub UI without doing tests, something might be broken now hah.

Will try this out with Windows changes

[rszyma]

Continued in #573