Eager Per Row Debouncing added (added to Ergodox) (#5498)

* Implemented Eager Per Row debouncing algorithm.

Good for when fingers can only press one row at a time (e.g. when keyboard is wired so that "rows" are vertical)

* Added documentation for eager_pr

* Ported ergodox_ez to eager_pr debouncing.

* Removed check for changes in matrix_scan.

* Added further clarification in docs.

* Accidental merge with ergodox_ez

* Small cleanup in eager_pr

* Forgot to debounce_init - this would probably cause seg-faults.

docs/feature_debounce_type.md

@@ -33,7 +33,10 @@ The debounce code is compatible with split keyboards.
 # Changing between included debouncing methods
 You can either use your own code, by including your own debounce.c, or switch to another included one.
 Included debounce methods are:
-* eager_pk - debouncing per key. On any state change, response is immediate, followed by ```DEBOUNCE_DELAY``` millseconds of no further input for that key
+* eager_pr - debouncing per row. On any state change, response is immediate, followed by locking the row ```DEBOUNCE_DELAY``` milliseconds of no further input for that row. 
+For use in keyboards where refreshing ```NUM_KEYS``` 8-bit counters is computationally expensive / low scan rate, and fingers usually only hit one row at a time. This could be
+appropriate for the ErgoDox models; the matrix is rotated 90°, and hence its "rows" are really columns, and each finger only hits a single "row" at a time in normal use.
+* eager_pk - debouncing per key. On any state change, response is immediate, followed by ```DEBOUNCE_DELAY``` milliseconds of no further input for that key
 * sym_g - debouncing per keyboard. On any state change, a global timer is set. When ```DEBOUNCE_DELAY``` milliseconds of no changes has occured, all input changes are pushed.