Allow compilation on Java 8

As at the moment many people will have Java 8, we should support Java 8 compilation.

I've compiled Alitheia on both Java 7 and 8 and with the update of FindBugs 0.0.3 and Antlr 3.5.2 it compiles again.

See also [https://github.com/antlr/antlr3/issues/151](https://github.com/antlr/antlr3/issues/151).