Merge pull request #3 from tbetbetbe/grpc-ruby-update-server-api

src/ruby/bin/interop/interop_server.rb

src/ruby/bin/math_server.rb

src/ruby/bin/noproto_server.rb

src/ruby/ext/grpc/rb_server.c

src/ruby/lib/grpc/generic/rpc_server.rb

src/ruby/spec/client_server_spec.rb

src/ruby/spec/generic/rpc_server_spec.rb

src/ruby/spec/server_spec.rb