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/da.c b/src/da.c
index a9bc696..8ff5bfa 100644
--- a/src/da.c
+++ b/src/da.c
@@ -6,7 +6,7 @@
 #include <haproxy/http.h>
 #include <haproxy/http_htx.h>
 #include <types/global.h>
-#include <proto/arg.h>
+#include <haproxy/arg.h>
 #include <proto/http_fetch.h>
 #include <proto/log.h>
 #include <proto/http_ana.h>