Fixed split_sstrings() when two separators were next to each other.
Fixed split_sstring() for when only 1 separator is found.
Added checks for when allocation goes wrong into split_sstring().
Changed split_sstring() to return str if no separator was found.
Improved a comment in split_sstring().
Created connect_sstrings().

The function basically connects all strings in the struct SStrings together and returns the result.
Added checks at the start of connect_sstrings().
Made connect_sstrings() able to add a connector between each string.
Improved a macro to have better argument names.
Made sure connect_sstrings() doesn't append connector to the end of the new string.
Added to_lower_sstring() and to_upper_sstring().