The regex handle to free.
Frees the memory associated with a regex result, and sets the handle to 0.
This must be called on all results from regex_match() when you are done extracting
the results with regex_substr().
The results of regex_compile() or regex_compile_ex() (and subsequently, regex_match_c())
only need to be freed when you are done using the pattern.
Do not use the handle again after freeing it!
This function has no return value.