[Linter] Add keyword linting

[totally-not-frito-lays]

Is your feature request related to a problem? Please describe.
In keywords.txt we declare a few keywords which the Arduino IDE uses for syntactic sugar.

Describe the solution you'd like
We should add a rule in the linter that whenever new library functions are written, they should be required to add in keywords of any new public functions declared.

Alternatively, we could run a github actions workflow to automatically generate a keyword commit each time a new .h file is created with public functions.

Describe alternatives you've considered
Already listed, need to determine which is the better option.

Additional context

• add RNG function keywords #47