Prototype k rewrite machine

I call it K rewrite machine but it's really just a simple interpreter so far. Eventually, this would become a a fast abstract rewrite machine and the starting point of native code generation.
In the Javadoc I explained that I had to retrieve indices from input/output cells different than k cell. It's just a workaround for now. I will implement the generic pattern match automata anyway in the future. And all these specific methods for handling different cells should all go away.