Add Hop-based Build System

Very Simple Hop-based Build System

**Implemented Stuff**:
- Documentation Generation
- Analyzer
- Bench Task
- Wrapper that runs 'pub get' when no packages/ directory exists.

**Things to Come**:
- Unit Testing
I generally avoid using parts. My preference would be for the parts to get moved into `tools/hop_runner.dart`; will ping @justinfagnani though.