Initial commit of the QtGstreamer helper code generator.

Initial commit of the QtGstreamer helper code generator.

This is a code generator that will parse QtGstreamer's
header files and will produce some extra code:
 * For each QGLIB_REGISTER_TYPE() macro, it will provide its
   QGLIB_REGISTER_TYPE_IMPLEMENTATION() counterpart.
 * For each defined enum, it will generate BOOST_STATIC_ASSERTs
   that will ensure that the values of the enums are exactly
   the same as in Gstreamer. This will help catch enum errors at
   compile time, since all Gstreamer's enums need to be redefined
   in the bindings to avoid exporting the Gstreamer API/ABI.