MINOR: http: add very simple header management based on double strings

This will be used initially by the hpack table and hopefully later by a
new native http processor. These headers are made of name and value, both
an immediate string (ie: pointer and length).
diff --git a/include/common/http-hdr.h b/include/common/http-hdr.h
new file mode 100644
index 0000000..a0bb341
--- /dev/null
+++ b/include/common/http-hdr.h
@@ -0,0 +1,50 @@
+/*
+ * HTTP header management (new model) - type definitions
+ *
+ * Copyright (C) 2014-2017 Willy Tarreau <willy@haproxy.org>
+ * Copyright (C) 2017 HAProxy Technologies
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+#ifndef _COMMON_HTTP_HDR_H
+#define _COMMON_HTTP_HDR_H
+
+#include <stdint.h>
+#include <common/ist.h>
+
+/* a header field made of a name and a value. Such structure stores 4 longs so
+ * it takes 16 bytes on 32-bit systems and 32 bytes on 64-bit systems.
+ */
+struct http_hdr {
+	struct ist n; /* name */
+	struct ist v; /* value */
+};
+
+/* sets an http_hdr <hdr> to name <n> and value <v>. Useful to avoid casts in
+ * immediate assignments.
+ */
+static inline void http_set_hdr(struct http_hdr *hdr, const struct ist n, const struct ist v)
+{
+	hdr->n = n;
+	hdr->v = v;
+}
+
+#endif /* _COMMON_HTTP_HDR_H */