add lua binding for the lxc API

The lua binding is based closely on the python binding. Also included are
a test program for excercising the binding, and an lxc-top utility for
showing statistics on running containers.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>