libctf: add new dynhash functions

libctf: add new dynhash functions

Future commits will use these.

ctf_dynhash_elements: count elements in a dynhash
ctf_dynhash_lookup_kv: look up and return pointers to the original key
                       and value in a dynhash (the only way of getting
                       a reference to the original key)
ctf_dynhash_iter_find: iterate until an item is found, then return its
                       key
ctf_dynhash_cinsert: insert a const key / value into a dynhash (a thim
                     wrapper in a new header dedicated to inline
                     functions).

As with the rest of ctf_dynhash, this is not public API.  No impact
on existing callers is expected.

libctf/
	* ctf-inlines.h: New file.
	* ctf-impl.h: Include it.
	(ctf_hash_iter_find_f): New typedef.
	(ctf_dynhash_elements): New.
	(ctf_dynhash_lookup_kv): New.
	(ctf_dynhash_iter_find): New.
	* ctf-hash.c (ctf_dynhash_lookup_kv): New.
	(ctf_traverse_find_cb_arg_t): New.
	(ctf_hashtab_traverse_find): New.
	(ctf_dynhash_iter_find): New.
	(ctf_dynhash_elements): New.