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/stream.c b/src/stream.c
index 530be55..151dbf0 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -34,7 +34,7 @@
 
 #include <proto/acl.h>
 #include <haproxy/activity.h>
-#include <proto/arg.h>
+#include <haproxy/arg.h>
 #include <proto/backend.h>
 #include <proto/channel.h>
 #include <proto/checks.h>