This commit adds support for server-side languages bindings.  This is done
in two ways:

1. Adding a wl_resource_set_dispatcher function that corresponds to
wl_resource_set_interface.  The only difference between the two functions
is that the new version takes a dispatcher along with the implementation,
data, and destructor.  This allows for runtime calling of native language
functions for callbacks instead of having to generate function pointers.

2. Adding versions of wl_resource_post_event and wl_resource_queue_event
that take an array of wl_argument instead of a variable argument list.
This allows for easier run-time argument conversion and removes the need
for libffi-based calling of variadic functions.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>