[MEDIUM] added the hdr_idx structure for future HTTP header indexing

This structure will consume 4 bytes per header to keep track of
headers within a request or a response without having to parse
the whole request for each regex. As it's not possible to allocate
only 4 bytes, we define a max number of HTTP headers. We set it
to (BUFSIZE+79)/80 so that 8kB buffers can contain 100 headers
(like Apache), resulting in 400 bytes dedicated to indexation,
or about 400/(2*8kB) ~= 2.4% of the memory usage.
diff --git a/Makefile b/Makefile
index 1eef960..f690a14 100644
--- a/Makefile
+++ b/Makefile
@@ -158,7 +158,7 @@
        src/time.o src/fd.o src/regex.o src/cfgparse.o src/server.o \
        src/checks.o src/queue.o src/capture.o src/client.o src/proxy.o \
        src/proto_http.o src/stream_sock.o src/appsession.o src/backend.o \
-       src/session.o
+       src/session.o src/hdr_idx.o
 
 haproxy: $(OBJS)
 	$(LD) $(LDFLAGS) -o $@ $^ $(LIBS)