REORG: http: move HTTP rules parsing to http_rules.c

These ones are mostly called from cfgparse.c for the parsing and do
not depend on the HTTP representation. The functions's prototypes
were moved to proto/http_rules.h, making this file work exactly like
tcp_rules. Ideally we should stop calling these functions directly
from cfgparse and register keywords, but there are a few cases where
that wouldn't work (stats http-request) so it's probably not worth
trying to go this far.
diff --git a/src/vars.c b/src/vars.c
index 905e20c..7cc06d6 100644
--- a/src/vars.c
+++ b/src/vars.c
@@ -7,6 +7,7 @@
 #include <types/vars.h>
 
 #include <proto/arg.h>
+#include <proto/http_rules.h>
 #include <proto/proto_http.h>
 #include <proto/sample.h>
 #include <proto/stream.h>