version to 2.7.0

* fixes to get the test suite passing in ree, mri, and rbx. (#183)
* add in rubysl gem dependency when running rbx (c7bf78f062716356d79c75a9df9811ed2e1e52e3)

Minor update b/c #183 above makes some previously protected context
setup dsl methods public.

/cc @jcredding