* Introduced a Lua implementation based on shelling out to a standard Lua binary.
* Bundled several Lua binaries for common platforms. I haven't added a 32-bit Linux binary yet, but that will come.
* Refactored the existing Lua class, bringing out functionality common to all Lua implementations into a set of common base classes.
* Moved the bulk of the implementation-specific functionality into a set of "interpreter" classes.
* Renamed LuaSandboxEngine to Scribunto_LuaSandboxEngine
* Don't create an engine object unconditionally when the ParserLimitReport hook is called.
* Implemented isolation of module global variable namespaces. This means that separate {{#invoke}} calls can't pass data to each other -- this was a desired feature in planning since it allows more flexibility in wikitext parser design. Isolation for mw.import() means that modules cannot accidentally create global variables which affect other modules -- exports are solely via the return value.
Change-Id: I3fa35651fe5b1fbfd85adeadc220b1ea31cd6f0b
