mpool: mpool now assert fails rather than returns NULL if a NULL is passed in as the ib_mpool_t*.
clipp: @parse (and thus most generators) now generates complete set of events, even if some of them are empty.
modhtp.c: Spell check.
CODESTYLE.md: Add section on callbacks.
docs: Add libhtp usage to DEVELOPMENT file.
Squashed 'libs/libhtp/' changes from c81e169..cdd75a8

cdd75a8 htp_transaction.c: Fix memory leak introduced in 6a82cbced8a3d76120ffb1f26ba9c38235a37ff9.
5bc26da htp_utf8_decoder.c: Remove 'inline' keyword for two functions that have external linkage but use statics.
ac76409 htp_request.c, htp_response.c: Fix use of uninitialized memory.

git-subtree-dir: libs/libhtp
git-subtree-split: cdd75a8354f4e96eb277392f8ed6a29be44ca322
libhtp: Sync with upstream 0.5.x.