Release Notes for CEL-Go v0.2.0

_Breaking changes_

* ref.TypeProvider FindType() use strings rather than proto Type object.
* cel.Vars() and cel.NoVars() have been deprecated in favor of passing
  a map directly. Certain alloc sensitive use cases may wish to provide
  their own interpreter.Activaiton to the cel.Eval() function.

_Improvements and fixes__

* Ability to restrict lists and maps to homogeneous types.
* Type isolation for for both runtime and check time.
* Bug fixes for data races and off-by-one errors.