This PR is a first attempt at introducing support for Lua 5.0, a version that some older games remain stuck on. It adds a 5.0 LuaTarget that triggers the appropriate syntax for variadic arguments and length-checking and modulo operations.

Lua 5.0, while mostly similar to 5.1, is not forwards-compatible; it is not possible to write a transpiler that is simultaneously compatible with both 5.0 and 5.1 syntax. Hence, if you choose to accept support for 5.0, you might also need to rename the "Universal" target to something more descriptive, like "5.1+".

Next steps: Adding tests, adding the appropriate type annotations for the 5.0 standard library to the lua-types package, and updating lualib to be 5.0-compatible.