Added ReadInteger()
Added a working ReadInteger implementation.
+ This requires a fake method to be inserted at the top of every Decaf class since the Java std lib is sufficiently braindead and Decaf doesn't have a linker.
+ [x] `io1.decaf` works
+ [x] `io3.decaf` works
Fix "unreachable code" Scalac warning
Fix bug where ReadLine() had the wrong type annotation (Closes #63)
+ [x] `io2.decaf` compiles