option parsing

[dcbaker]

Implement option parsing. This will involve turning the frontend on the options, then lowering them from ast into something different, then parsing the options from the command line, and storing them in the resistant state. for some options that will be pretty easy, for others it will be harder.

My current thought is that we'll do something like:

1. DSL -> AST (shared with current passes)
2. AST -> MIR (shared with current passes)
3. Custom pass to reduce option() calls into something more like what we want
4. store those options (this would be a good place to cache something to avoid 1..3 on rebuilds)