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