libxl: Introduce JSON parser

We use the yajl parser, but we need to make a tree from the parse result
to use it outside the parser.

So this patch include json_object struct that is used to hold the JSON
data.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Committed-by: Ian Jackson <ian.jackson.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

README

@@ -47,6 +47,7 @@ provided by your OS distributor:
     * Development install of openssl (e.g., openssl-dev)
     * Development install of x11 (e.g. xorg-x11-dev)
     * Development install of uuid (e.g. uuid-dev)
+    * Development install of yajl (e.g. libyajl-dev)
     * bridge-utils package (/sbin/brctl)
     * iproute package (/sbin/ip)
     * hotplug or udev