code: public FunctionList signatureStartsWith(final Class... args) {
          return filter(new Filter() {
              public boolean keep(Function m) {
                  Class[] params = m.getParameterTypes();
                  if(params.length<args.length)  return false;
                  for( int i=0; i<args.length; i++ ) {
                      if(params[i]!=args[i])
                          return false;
                  }
                  return true;
              }
          });
      }
docs: Returns {@link Function}s that has the parameters
  that start with given types (but can have additional parameters.)