feat: implemented an alt-repeat key

[Nuclear-Squid]

Describe your changes. Use imperative present tense.

Implemented an alt-repeat key. It functions the same as the standard repeat key, but takes in a list of pairs of keycodes to give substitutions. For instance, you can repeat keys as usual, but send e instead of d when repeating the d key.

A possible use-case for such a feature is to implement the "magic key" from Magic-Sturdy

Disclaimer : I am not a native English speaker, I am sorry if there are typos in the docs ^^'

Checklist

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

[Nuclear-Squid]

This implementation only allows simple KeyCode -> KeyCode substitutions, which is still pretty limited. It’s not possible to repeat macros for instance (or alt-repeat a symbol with a macro), and rpt doesn’t seem to work with sequences (a sequence gg isn’t detected if you type it as g rpt). I’d like to help make that system more flexible, would you be interested in that ?

[jtroo]

Thanks for the contribution! Could you comment on the advantages of this action over switch?

https://jtroo.github.io/config.html#switch