Update: Conversion should return F_number_positive and F_number_negative without...

Update: Conversion should return F_number_positive and F_number_negative without error bit and do some clean up.

Do not treat F_number_positive and F_number_negative as an error.
The "unsigned" concept should be internal to the function and not whether or not the user input has a sign.

If F_number_negative is returned, the value can still be of type f_number_unsigned_t.
This is because the return status designates the effective sign.
The caller can then decide whether or not this is an error.