Update: The f_utf project regarding digits and perform other clean ups.

Update: The f_utf project regarding digits and perform other clean ups.

Redesign the digit and decimal behavior.
The is digit functions now refers to base-10 but does not attempt to return the identified digit.
The is decimal functions now refers to base-10 and supports providing the identified digit.
The is decimal functions also support other base units than just base-10.

The alphabetic digit/numeric functions now also have a alphebetic decimal function.

Clean up more places in the code using "sequence" rather than "character" or "characters".

Functions like f_utf_character_is_alpha_digit() are now like f_utf_character_is_alphabetic_digit().

Add related unit tests.
The is digit functions have unit tests that tests if the digit returned is correct.
I have not reviewed all of the "numeric" Unicode digits to confirm/deny that my is decimal functions are complete.

I observed what looks like bugs in the alphabetic functions.
In these cases the final return statement is returning F_false when they instead should be returning F_true.

There are minor corrections in documentation.