Instead of cumbersome field list mamangement, we will tokenize input
using custom `bdf_strtok_`.
* src/bdf/bdflib.c (bdf_list_t_, bdf_list_init_, bdf_list_ensure_,
bdf_list_shift_, bdf_list_join_, bdf_list_split_,
bdf_set_default_spacing_): Removed.
(bdf_strtok_): New function which NUL-terminates the first token at
the delimiter position and returns the next token that follows
consequtive delimiters.
(bdf_parse_*_, bdf_load_font): Updated.
* docs/CHANGES: Claim overall 75% performance improvement.
01c22b3668