Interface persistence, the sane way.

I'm saving an interface to the corresponding module's class file by
using a custom "jelly.iface" class attribute. This attribute holds the
byte array resulting from serializing the interface. 

This *way* better than using a byte[] static field, since:

  1. Reading the interface doesn't require passing the module class thru
     a class loader in order to execute <clinit> (so I don't need the
     whole runtime in the classpath)
  2. Storing the raw bytes in an attribute is much more space friendly
     than adding the bytecode instructions to initialize a byte array.
     We end up with much smaller module class files.