add register names to allocator

make platform instantiate it
basic plumbing

lib/risc/platform.rb

@@ -8,14 +8,26 @@ module Risc
     # return the translator instance that traslates risc intructions into
     # platform specific ones
     def translator
+      raise "not implemented"
     end
 
     # return an integer where the binary is loaded
     def loaded_at
+      raise "not implemented"
     end
 
     # return the number of registers the platform supports
     def num_registers
+      raise "not implemented"
+    end
+
+    # return the Allocator for the platform
+    # stanrard implementation return StandardAllocator, which uses
+    # num_registers and assumes rXX naming (ie arm + interpreter)
+    #
+    # Possibility to override and implemented different schemes
+    def allocator(compiler)
+      StandardAllocator.new(compiler , self )
     end
 
     # Factory method to create a Platform object according to the platform