Use supplied getopt.

(werror): New function.
(sexp_output_hash_init): New function.
(sexp_put_char): Made base64 linebreaking configurable.
Implemented hashing.
(sexp_put_code_start, sexp_put_code_end): Don't output any
delimiters here.
(sexp_put_string): Output base64 delimiters.
(sexp_put_digest): New function.
(sexp_convert_item): Output transport delimiters.
(sexp_convert_file): Deleted function, folded with main.
(parse_options): New function.
(main): Implemented --hash and --once, needed by lsh-authorize.

Rev: src/nettle/tools/sexp-conv.c:1.2