* doc/chew.c (delete_string): Only free the string buffer if it is
there. Mark the buffer as NULL after freeing.
(drop): Free the dropped string.
(free_words): New function: Frees the memory allocated to the
dictionary.
(add_instrinsic): Duplicate the name string, so that it can be
freed later on.
(compile): Free unused words.
(main): Free the dictionary and top level string buffers at the
end.