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

Well, I didn't manually add the scala-xml library, but maybe it's contained in one of the other jars in the classpath. I don't particularly care if we remove that file, but we should replace it with something else. It was basically the first moderate-sized and self-contained scala snippets I fond online so I went with it. If you have other (better) such resources you can point me to, I'll gladly remove this one.