Made ActionView::Base#first_render a little more private. And added _last_render to track the most recent render. Will fix #609 as a side effect. [#609 state:resolved]

Refactor template preloading. New abstractions include Renderable mixins and a refactored Template class.

Changed ActionView::TemplateHandler#render API method signature to render(template, local_assigns = {})

Added local assign keys to compiled method name so two threads evaluating the same template with different locals don't step on top of each other

Lookup compiled methods in CompiledTemplates instance methods set instead of using a "methods_names" hash