rename register to risc

seems to fit the layer much better as we really have a very reduced
instruction set

lib/risc/builtin/space.rb

@@ -0,0 +1,25 @@
+require "ast/sexp"
+
+module Risc
+  module Builtin
+    class Space
+      module ClassMethods
+        include AST::Sexp
+
+        # main entry point, ie __init__ calls this
+        # defined here as empty, to be redefined
+        def main context
+          compiler = Vm::MethodCompiler.create_method(:Space , :main ).init_method
+          return compiler.method
+        end
+
+      end
+      extend ClassMethods
+    end
+  end
+end
+
+require_relative "integer"
+require_relative "object"
+require_relative "kernel"
+require_relative "word"