Extract DSL::Evaluator from existing DSLs

Both the Modulefile and Puppetfile DSL classes implemented this
functionality duplicately. This forces standardization of behavior
between all DSLs while DRYing up behavior.
Privatize more DSL::Evaluator methods
Add tomdocs for DSL::Evaluator
Extract DSL::Evaluator#short_class_name
Mark DSL::Evaluator.evaluate and #evaluate as internal methods
Merge pull request #6 from wfarr/dsl-evaluate-refactoring

Extract DSL::Evaluator from existing DSLs
Extract #handle_syntax_error and #handle_other_parse_error from DSL::Evaluator#evaluate
Memoize more values in DSL::Evaluator just to be safe
Reduce the complexity in Henson::Installer with some method extraction
Merge branch 'master' of https://github.com/wfarr/henson into extract-api-client

Conflicts:
	lib/henson.rb
Add tomdocs to Henson