Add Ravi Compiler as a lib

[dibyendumajumdar]

The goal of this is to start generating JIT code from Lua Source rather than Lua Bytecodes as we have been doing until now. We will leverage the new (WIP) compiler project for Ravi - https://github.com/dibyendumajumdar/ravi-compiler.

This approach will have following potential benefits.

a) We can hopefully generate better code as we would no longer be constrained by Lua bytecodes
b) We can define our own IR and benefit from optimizations such as inlining.
c) We can also support AOT mode I think.