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/ssl_sample.c b/src/ssl_sample.c
index 5f8cbd7..8eb958b 100644
--- a/src/ssl_sample.c
+++ b/src/ssl_sample.c
@@ -29,7 +29,7 @@
 #include <types/ssl_sock.h>
 
 #include <proto/acl.h>
-#include <proto/arg.h>
+#include <haproxy/arg.h>
 #include <proto/obj_type.h>
 #include <proto/ssl_sock.h>
 #include <proto/ssl_utils.h>