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

I wonder if this introduces some complexity due to xml. Don't you need to add `scala-xml` to the test classpath? Just wondering if this isn't going to prove fragile in the face of Scala (xml) evolution.