cross compile for 2.11.1; drop support for 2.9.x

- Upgrade to ScalaTest 2.1.6
- Update matchers to be compatible with Manifest requirements of
  scala-parser-combinators library
move safeParent to Context class
extract contextFactory; favor composition over inheritance
move TruthValue to context; declare model for what it is: Any
separate Context and ContextFactory
move value interpretation methods to context
Extract databinding concerns from Context
allow different binding strategies via implicit BindingFactory

- Propagate the use of binding throughout Handlebars-scala (IfHelper, EachHelper, etc. use them operate on values)
- Clean decoupling between which data to access and how to access it