* Fix overflow in WPM calculations.
First, the "fresh" WPM calculation could end up being up to 12000 (with
default `WPM_ESTIMATED_WORD_SIZE`) if keys were pressed more or less
simultaneously. This value has now been clamped down to 255, in effect
clamping WPM to its max value of 255.
Second, with `WPM_ALLOW_COUNT_REGRESSION` enabled, it was possible to
regress the WPM below 0 (i.e. to 255) by just repeatedly pressing
backspace.
* Fix WPM being limited to 235 due to float/int logic.
Joakim Tufvegren