REORG: http: move the HTTP/1 chunk parser to h1.{c,h}

REORG: http: move the HTTP/1 chunk parser to h1.{c,h}

Functions http_parse_chunk_size(), http_skip_chunk_crlf() and
http_forward_trailers() were moved to h1.h and h1.c respectively so
that they can be called from outside. The parts that were inline
remained inline as it's critical for performance (+41% perf
difference reported in an earlier test). For now the "http_" prefix
remains in their name since they still depend on the http_msg type.