There is no single obvious form for a set in lua, and it is not very difficult
to accept a table and convert the sequence values into a set.
Also rename some methods as per discussion.
When talking about "loading" Lua code, it usually means compiling a
chunk of code into a runnable Lua function, but without actually
running it. This makes that clear.
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.