Include <stdbool.h>.

Include <stdbool.h>.
(readtoken): Use `size_t' rather than int/long.
All callers adjusted.
Use `bool' rather than `int' where appropriate.
Use memset rather than an explicit loop.
Use x2nrealloc rather than xrealloc.
Allow the use of `\0' as a delimiter.
(readtokens): Likewise.