Implement: refinement type check

[baban]

I evaluate RDL now and I notice that some functions lack yet.
so, I try to implement Refinement, because I wanto to use it.

I use like below code.

module ArrayExtention
 refine do
   extend RDL::Annotate
   refine_type '()->String'
   def foo
     [].to_s
   end
 end
end
using_type ArrayExtention

I declare refine_type and using_type method.
It is nessesary now.

I'm writing README.md now.

I expect some function (for exmple method_missing) will support in future.