Update: Add missing function in f_utf needed for completeness and reduce repeated...

Update: Add missing function in f_utf needed for completeness and reduce repeated code.

As per my completeness principle, the f_utf_unicode_string_to() must have the f_utf_character_unicode_string_to() compliment.
This function only allows for ASCII characters to represent the number and returns errors as appropriate for non-ASCII values.
Unicode number values are not treated as the ASCII numbers for representing a Unicode code sequence.

The f_utf_character_unicode_to() and f_utf_unicode_to() now has code reduced by utilizing private_f_utf_character_unicode_to().