Provide default implementation of accept method
add leave method to visitor
add test for visiting abstract method
add test for visiting this in RHS
Merge branch 'linzhp-missing_accepts'
Fixed python 3.4 compatibility
Replaced a second instance of open()
Merge pull request #27 from computer-whisperer/master

Switched instances of file() to open() to allow the parser to run in python 3.4