MINOR: hpack: implement the HPACK Huffman table decoder

The code was borrowed from the HPACK experimental implementations
available here :

    https://github.com/wtarreau/http2-exp

It contains the Huffman table as specified in RFC7541 Appendix B, and a
set of reverse tables used to decode a Huffman byte stream, and produced
by contrib/h2/gen-rht. The encoder is not finalized, it doesn't emit the
byte stream but this is not needed for now.

Makefile

@@ -848,6 +848,7 @@ OBJS = src/cfgparse.o src/proto_http.o src/stats.o src/server.o src/stream.o \
        src/haproxy.o src/stream_interface.o src/tcp_rules.o src/proxy.o \
        src/listener.o src/acl.o src/flt_http_comp.o src/filters.o src/dns.o \
        src/cli.o src/flt_trace.o src/connection.o src/session.o src/vars.o \
+       src/hpack-huff.o \
        src/map.o src/payload.o src/namespace.o src/compression.o \
        src/mailers.o src/auth.o src/proto_udp.o src/memory.o src/freq_ctr.o \
        src/signal.o src/uri_auth.o src/buffer.o src/task.o src/chunk.o \

include/common/hpack-huff.h

@@ -0,0 +1,35 @@
+/*
+ * Huffman decoding and encoding for HPACK (RFC7541)
+ *
+ * Copyright (C) 2014-2017 Willy Tarreau <willy@haproxy.org>
+ * Copyright (C) 2017 HAProxy Technologies
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+#ifndef _PROTO_HPACK_HUFF_H
+#define _PROTO_HPACK_HUFF_H
+
+#include <stdint.h>
+
+int huff_enc(const char *s, char *out);
+int huff_dec(const uint8_t *huff, int hlen, char *out, int olen);
+
+#endif