REORG: include: create new file haproxy/api-t.h

This file is at the lowest level of the include tree. Its purpose is to
make sure that common types are known pretty much everywhere, particularly
in structure declarations. It will essentially cover integer types such as
uintXX_t via inttypes.h, "size_t" and "ptrdiff_t" via stddef.h, and various
type modifiers such as __maybe_unused or ALIGN() via compiler.h, compat.h
and defaults.h.

It could be enhanced later if required, for example if some macros used
to compute array sizes are needed.
diff --git a/include/haproxy/api-t.h b/include/haproxy/api-t.h
new file mode 100644
index 0000000..501f4ad
--- /dev/null
+++ b/include/haproxy/api-t.h
@@ -0,0 +1,39 @@
+/*
+ * include/haproxy/api-t.h
+ * This provides definitions for all common types or type modifiers used
+ * everywhere in the code, and suitable for use in structure fields.
+ *
+ * Copyright (C) 2020 Willy Tarreau - w@1wt.eu
+ *
+ * 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 _HAPROXY_TYPES_H
+#define _HAPROXY_TYPES_H
+
+#include <inttypes.h>
+#include <stddef.h>
+
+#include <common/compat.h>
+#include <common/compiler.h>
+#include <common/defaults.h>
+
+#endif /* _HAPROXY_TYPES_H */