Fixed a bad check.
Fixed compare_n_sstring() not working if num was lower than length.
Improved free_sstring() to also set the pointer to NULL after freeing it.
Added parantheses in free_sstring() so it resolves correctly.
Changed free_sstrings() to also NULL the freed pointer.
Changed free_sstring() to make more sense.
Fixed copy_string_to_sstring not copying all the characters.
Fixed two functions returning negative of what they should.
Fixed find_chars_in_sstring() calling the wrong function inside itself.