REORG: include: move arg.h to haproxy/arg{,-t}.h

Almost no change was needed; chunk.h was replaced with buf-t.h.
It dpeends on types/vars.h and types/protocol_buffers.h.
diff --git a/src/frontend.c b/src/frontend.c
index 8206709..a71dc09 100644
--- a/src/frontend.c
+++ b/src/frontend.c
@@ -30,7 +30,7 @@
 #include <types/global.h>
 
 #include <proto/acl.h>
-#include <proto/arg.h>
+#include <haproxy/arg.h>
 #include <proto/channel.h>
 #include <haproxy/fd.h>
 #include <proto/frontend.h>