Move test files' extentions from .txt to .hs

typechecker/test/Main.hs

typechecker/test/cases/parser/arityFour-parser.hs

typechecker/test/cases/parser/leftPlusTwo-parser.hs

typechecker/test/cases/parser/myId-check-parser.hs

typechecker/test/cases/parser/myNot-parser.hs

typechecker/test/cases/parser/myOr-infer-parser.hs

typechecker/test/cases/parser/notOfNot-parser.hs

typechecker/test/cases/parser/plusPlus-parser.hs

typechecker/test/cases/parser/unwrapMaybeBool-parser.hs

typechecker/test/cases/should-fail/repeatInvisTyAbs.hs

typechecker/test/cases/should-fail/repeatVarPatInfer.hs

typechecker/test/cases/should-typecheck/Just-3-tuple-pb.hs

typechecker/test/cases/should-typecheck/JustXfmap.hs

typechecker/test/cases/should-typecheck/absMaybe.hs

typechecker/test/cases/should-typecheck/absMaybeMaybe.hs

typechecker/test/cases/should-typecheck/addMaybeInt-cases.hs

typechecker/test/cases/should-typecheck/appOne-QL.hs

typechecker/test/cases/should-typecheck/blah-infer.hs

...ecker/test/cases/should-typecheck/bool-functions-infer.hs

typechecker/test/cases/should-typecheck/break-infer.hs