partially for the selfish reason that my submodule setup does not deal well with
ureleased versions of cargo libs where the version number ends with -pre
Allow load to return values, allows reimplementing require() like functions
properly.
Make globals table explicit in Lua, remove Lua::get / Lua::set in favor of
Lua::globals. Allows obeying globals metatable, using other Table functions on
the globals table.
Also added "has" method as shorthand for checking whether a table entry is not
nil.
kyren