introduce platform to abstract cpu and load address

lib/risc/platform.rb

@@ -0,0 +1,28 @@
+module Risc
+  # A platform is (or will be) something like the linux tripple
+  #
+  # Currently it just provides a Translator and binary start point
+  #
+  class Platform
+
+    # return the translator instance that traslates risc intructions into
+    # platform specific ones
+    def translator
+    end
+
+    # return an integer where the binary is loaded
+    def loaded_at
+    end
+    # Factory method to create a Platform object according to the platform
+    # string given.
+    # Currently only "Arm"
+    def self.for( name )
+      case name
+      when "Arm"
+        return Arm::ArmPlatform.new
+      else
+        raise "not recignized platform #{name}"
+      end
+    end
+  end
+end