* Refactor to enable optimizer modules
This refactors HMX compilation into steps:
1. Parse - Turn HMX string into an AST.
2. Optimize - Walk the AST making modifications.
3. Codegen - Turn the AST into hyperscript function calls.
There's still more logic in (3) than we probably want. The nice there here is it gives a Visitor API that you can implement to do optimizations. See src/optimize/styles.ts for an example.
* Allow multiple visitors per optimizer
This adds parse error in a nicely formatted way, and moves the existing console.logs into a fork of the Snowpack logger. The new logger is not a singleton and won't preformat the message.
