MINOR: http_htx: Add functions to manipulate HTX messages in http_htx.c

This file will host all functions to manipulate HTTP messages using the HTX
representation. Functions in this file will be able to be called from anywhere
and are mainly related to the HTTP semantics.
diff --git a/include/types/http_htx.h b/include/types/http_htx.h
new file mode 100644
index 0000000..c8f4197
--- /dev/null
+++ b/include/types/http_htx.h
@@ -0,0 +1,37 @@
+/*
+ * include/types/http_htx.h
+ * This file defines everything related to HTTP manipulation using the internal
+ * representation.
+ *
+ * Copyright (C) 2018 HAProxy Technologies, Christopher Faulet <cfaulet@haproxy.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, version 2.1
+ * exclusively.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+#ifndef _TYPES_HTTP_HTX_H
+#define _TYPES_HTTP_HTX_H
+
+#include <common/ist.h>
+#include <types/htx.h>
+
+/* Context used to find/remove an HTTP header. */
+struct http_hdr_ctx {
+	struct htx_blk *blk;
+	struct ist     value;
+	uint16_t       lws_before;
+	uint16_t       lws_after;
+};
+
+#endif /* _TYPES_HTTP_HTX_H */