48ff93582b
Instead of having all sendstring keycode mappings in the main quantum.c file, give each one its own file in keymap_extras that can be #included in a user's keymap. If one is included, it will define the appropriate lookup tables and overwrite the weak definitions in quantum.c. (Including more than one sendstring definition will fail at compile time.) Update @rai-suta's test keymap to match, as well as the documentation.