Now using the '==' and '!=' operators instead of instanceof and getClass().
Changed the typechecker so it doesn't throw exceptions but appends errors to an error list.
Modified tests so they also use the error list instead of exceptions.
Merge branch 'JessevanAssen-master'

Conflicts:
	JessevanAssen/src/org/uva/sea/ql/typechecker/TypecheckerVisitor.java
Merge branch 'master' of https://github.com/software-engineering-amsterdam/sea-of-ql
Prettyprinter finished
second commit
Single 
Added binary and unary classes, added value for int and made basic + - and * operations and some tests
Added tests and updated checker
Merge branch 'martyn82'
Merge branch 'master' of github.com:software-engineering-amsterdam/sea-of-ql