allow user to provide regex object storage

[marler8997]

I've added a new function re_compile_to that takes a pointer to an array of objects and characters. This allows a user to specify their own storage for their regex objects. This way a user can compile multiple regex objects and keep them around if they so choose. At the same time this also means that the user will need to know the value of MAX_REGEXP_OBJECTS and MAX_CHAR_CLASSLEN, so I made those configurable by putting them inside their own #ifdefs. This way a user can customize them with -DMAX_REGEXP_OBJECTS=XXX and -DMAX_CHAR_CLASS_LEN=YYY.

Note that if #62 is accepted, this we won't need to expose the regex_t struct in re.h. So maybe we should decide on #62 first?

[marler8997]

shoot I just realized this won't work because the user doesn't have access to the definition of regex_t, so they can't create an array of them

EDIT: I added a 2nd commit to make this work by moving the definition of regex_t into re.h.

[marler8997]

I've added a 2nd commit that moves the definition of regex_t into re.h. This way the user knows the size of the regex_t so it can manage its own storage of them.

[marler8997]

If this is accepted, one more addition I would suggest is a way to query the size of a compiled regex. This way, one could compile a regex, then afterward check how many objects and characters is is using, then allocate the exact storage required and re-compile them into the new storage location.

[skyformat99]

good