Coq backend

Java side of the Coq backend. A statically linked binary is further ahead on bmmoore/k@cbdb4f79fdbc
I set the java flag because I'm aiming to support features closer to the Java backend than the Maude backend, and the flag seems to be used in various places to type things as KItem rather than K and so on.
The last flag is set to false because I don't make a `-kompiled` directory, I just put the generated `.v` files next to the `.k` files. I wouldn't terribly mind changing it, but I think it makes sense not to hide them away because you will presumably have other Coq files proving things based on the definition, and also for now you need to manually supply a bit of scaffolding to go with the generated files.