Refactor project to allow usage of both Lua and Rust logic

[dasupradyumna]

Context

The library crate that is created by the current Rust source code is designed to be directly accessed in Lua as require('launch'), with the API as functions in this module. This has the limitation that all plugin has to be within Rust code, and any auxillary Lua / VimL code cannot be cleanly added if needed in the future.

A refactor of the project design is required that will support plugin development from both Lua and Rust code.