Function: type-break-guesstimate-keystroke-threshold

Guess values for the minimum/maximum keystroke threshold for typing breaks.

If called interactively, the user is prompted for their guess as to how
many words per minute they usually type. This value should not be your
maximum WPM, but your average. Of course, this is harder to gauge since it
can vary considerably depending on what you are doing. For example, one
tends to type less when debugging a program as opposed to writing
documentation. (Perhaps a separate program should be written to estimate
average typing speed.)

From that, this command sets the values in `type-break-keystroke-threshold'
based on a fairly simple algorithm involving assumptions about the average
length of words (5). For the minimum threshold, it uses about a fifth of
the computed maximum threshold.

When called from Lisp programs, the optional args WORDLEN and FRAC can be
used to override the default assumption about average word length and the
fraction of the maximum threshold to which to set the minimum threshold.
FRAC should be the inverse of the fractional value; for example, a value of
2 would mean to use one half, a value of 4 would mean to use one quarter, etc. (fn WPM &optional WORDLEN FRAC)