Changed all related functions to take a struct nettle_buffer *
argument instead.
(struct sexp_compound_token): New struct.
(sexp_compound_token_init, sexp_compound_token_clear): New
functions.
(struct sexp_parser): Added a struct sexp_compound_token
attribute, as a temporary measure.

Rev: src/nettle/tools/sexp-conv.c:1.11