Abide verification framework

First internal release of the abide framework that features:
- reflective rule and analyzer loading
- abide compiler plugin
- basic cli that provides 4-phase compilation with abide on top
- sbt plugin sketch (needs version management)
- traversal analyzer that applies single-traversal rules
- scoping analyzer that applies single-traversal rules and provides scoping and/or path information
- a few example rules and doc on how to add more

Yep, all error/warning reporting should go through `global.reporter` (`reporter.error` / `reporter.warning`). I prefer `assert` for internal sanity checking.