Clean-up the CCL API. Moved some internal structures from ccl.h to

Clean-up the CCL API. Moved some internal structures from ccl.h to
private header cclp.h. Changed ccl_parser_create so that a Bibset must
be supplied. Removed tokenize API from ccl.h - including ccl_parser_find.
This is replaced by ccl_parser_find_str which takes a string instead.