MINOR: http_htx: Add functions to manipulate HTX messages in http_htx.c

This file will host all functions to manipulate HTTP messages using the HTX
representation. Functions in this file will be able to be called from anywhere
and are mainly related to the HTTP semantics.
diff --git a/Makefile b/Makefile
index 33f70e9..b4125e1 100644
--- a/Makefile
+++ b/Makefile
@@ -924,7 +924,7 @@
        src/mailers.o src/h2.o src/base64.o src/hash.o src/http.o	\
        src/http_acl.o src/http_fetch.o src/http_conv.o src/http_act.o   \
        src/http_rules.o src/proto_sockpair.o src/proto_htx.o            \
-       src/mux_h1.o src/htx.o
+       src/mux_h1.o src/htx.o src/http_htx.o
 
 EBTREE_OBJS = $(EBTREE_DIR)/ebtree.o $(EBTREE_DIR)/eb32sctree.o \
               $(EBTREE_DIR)/eb32tree.o $(EBTREE_DIR)/eb64tree.o \