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 know this is my fault for not providing tests, but a few tricky cases we should add at some point:

* not reporting false positives in
  *  `(_, _) => ...` params like `x$1` are created for those anonymous parameters
  * constructor parameters used only in super constructor: `class Foo(x: Int) extends Super(x)`
* unused constructor parameters *should* be treated correctly when used/not used in body
* user-defined binders in case classes