Add isList() and toList() to ExpressionNode

To complement the existing isLiteral() and toLiteral() methods.
Add test for the toList and isList methods
Use AstConstructionHelper in AstTest class
Merge pull request #4 from cljc/ast-expression-aslist

Add methods to AST classes to convert to list expressions
Hack in error gathering and reporting

Pretty primitive still
Use ParseErrors instead of Strings and add a unit test
Move SchemeFile.hasErrors to the proper location in the file
Move ANTLR parser stuff into method in SchemeFile
Use new SchemeFile method in AstConstructionHelper
Refactor and clean up error reporting

Use proper ErrorListener interface
Merge pull request #5 from cljc/parse-error-notification

Improve error reporting
Begin implementing a graph framework
Merge branch 'graph' of https://github.com/cljc/cljc into graph