Make the compiler less tightly coupled to the CLI

[MatthewKosloski]

The CLI should simply be a wrapper around the compiler. That is, the compiler code should be loosely coupled from the command-line arguments. For instance, instead of keeping a reference to a TorreyConfig object, the TorreyCompiler constructor should have arguments (see here).

[MatthewKosloski]

At torrey/src/main/java/me/mtk/torrey/, make a new package compiler to hold packages frontend and backend. Then, create a sibling interface package to contain all the command-line interface code.

[MatthewKosloski]

Maybe even try to implement our own command-line parser (similar to how they do it in TypeScript) instead of relying on jcommander

[MatthewKosloski]

By less tightly coupled, I mean the core compiler should expose an API to the CLI, which would be the interface between the user of the compiler and the compiler itself.

[MatthewKosloski]

Closing this as issue #15 takes care of this and more