Add LuaJIT benchmark

[stephanos]

Feel free to merge or ignore this, just thought I'd share my change :)

[khvzak]

There are no benefics in LuaJIT for this specific test case.
LuaJIT does not perform any jit optimizations when working with Lua C API, and instead requires C ffi to work effectively.

[stephanos]

You see, I didn't know that; and this benchmark might help to illustrate your point to people like me.
In any case, feel free to merge or close :)

[rohitjoshi]

Agree. I still think it is worth merging as people who are used to LuaJIT would like to understand relative performance.