* src/ntbtls.h.in (ntbtls_log_handler_t): New type.
(ntbtls_set_log_handler): New.
* src/visibility.c (ntbtls_set_log_handler): New.
* src/visibility.h (ntbtls_set_log_handler): Mark visible.
* src/libntbtls.def: Add ntbtls_set_log_handler.
* src/libntbtls.vers: Add ntbtls_set_log_handler.
* src/debug.c (log_handler, log_handler_value): New vars.
(_ntbtls_set_log_handler): New.
(_ntbtls_set_debug): Do not re-set the prefix.
(_ntbtls_debug_msg): Divert to a log handler.
* src/util.c (_ntbtls_trim_trailing_spaces): New.
(ascii_toupper): New.
(_ntbtls_ascii_strcasecmp): New.
* src/util.h (spacep, digitp, alphap, alnump, hexdigitp): New macros.
(ascii_isspace): New macro.
(atoi_1, atoi_2, atoi_4, xtoi_1, xtoi_2, xtoi_4): New macros.