add register names to allocator

make platform instantiate it
basic plumbing

test/risc/test_platform.rb

@@ -12,5 +12,9 @@ module Risc
     def test_factory_raise
       assert_raises{ Platform.for("NotArm")}
     end
+    def test_allocate
+      allocator = Platform.new.allocator(FakeCompiler.new)
+      assert_equal FakeCompiler , allocator.compiler.class
+    end
   end
 end

test/risc/test_standard_allocator.rb

@@ -16,6 +16,9 @@ module Risc
     def test_empty
       assert @allocator.used_regs_empty?
     end
+    def test_reg_names
+      assert_equal 16 , @allocator.reg_names.length
+    end
     def test_compiler
       assert_equal CallableCompiler , @allocator.compiler.class
       assert_equal :fake_name , @allocator.compiler.callable.name