enable mission scripting with LuaJIT

[melvinzhang]

Over at the discord, I noticed there is interest in modding the game in various ways. One of them is to add custom missions. There are certain parts of the code that isn't performance sensitive, such as mission setup and I think these parts would benefit from scripting so it can be dynamically changed without recompiling the binary.

In https://github.com/melvinzhang/liberation-circuit/tree/lua I'm experimenting with integrating LuaJIT by converting some of the missions to be created using Lua code. The lua version looks like this: https://github.com/melvinzhang/liberation-circuit/blob/lua/bin/story/green/green2/green2.lua

So far, I've got it working on Linux, requiring the install of libluajit-5.1-dev package and building with -lluajit-5.1

Would this be something that you'd consider merging?