A macro that embeds a lua source tree on disk into the binary, similarly to how include_str!
can include a single file. Called like include_lua!("name": "path"), where name is a label
that appears in lua stacktraces involving code loaded from the tree, and path specifies a folder
relative to src/ in which the tree can be found. name defaults to path if omitted.
A piece of UserData that acts like a Lua searcher.
When called as a function with a single string parameter, attempts to load
(but not execute) a module by that name. If no module is found, returns nil.