fixing a small number of errors for tests, like issue with neg
readPairs added
Correct output file name
src/antlr
Merge branch 'backend' of https://gitlab.doc.ic.ac.uk/lab1314/wacc_37 into backend
didn't need to do the type checking and it was breaking things, so have removed
Refactoring BackEnd. TODO: Extract helper methods into separate class.
Merge with origin/backend. Conflicts not resolved.