stand: liblua: add a pager module

This is nearly a 1:1 mapping of the pager API from libsa. The only real
difference is that pager.output() will accept any number of arguments and
coerce all of them to strings for output using luaL_tolstring (i.e. the
__tostring metamethod will be used).

The only consumer planned at this time is the upcoming "show-module-options"
implementation.

MFC after: 1 week