Add respond_to_missing?

Hello! This probably doesn't affect a huge number of people, but I ran across a problem in a project I'm working on that was caused by a Draper decorator object not returning a delegated method when I queried it using #method. I patched it by including respond_to_missing? methods for both instances and classes. Since respond_to_missing? seems only to have appeared in Ruby 1.9.2, I guarded the code against evaluating in earlier versions of Ruby.