Add FieldMask demo method

Makefile

@@ -27,18 +27,21 @@ generate:
		--gogo_out=plugins=grpc,\
Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,\
Mgoogle/protobuf/empty.proto=github.com/gogo/protobuf/types,\
Mgoogle/api/annotations.proto=github.com/gogo/googleapis/google/api:\
Mgoogle/api/annotations.proto=github.com/gogo/googleapis/google/api,\
Mgoogle/protobuf/field_mask.proto=github.com/gogo/protobuf/types:\
$$GOPATH/src/ \
		--grpc-gateway_out=\
Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,\
Mgoogle/protobuf/empty.proto=github.com/gogo/protobuf/types,\
Mgoogle/api/annotations.proto=github.com/gogo/googleapis/google/api:\
Mgoogle/api/annotations.proto=github.com/gogo/googleapis/google/api,\
Mgoogle/protobuf/field_mask.proto=github.com/gogo/protobuf/types:\
$$GOPATH/src/ \
		--swagger_out=third_party/OpenAPI/ \
		--govalidators_out=gogoimport=true,\
Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,\
Mgoogle/protobuf/empty.proto=github.com/gogo/protobuf/types,\
Mgoogle/api/annotations.proto=github.com/gogo/googleapis/google/api:\
Mgoogle/api/annotations.proto=github.com/gogo/googleapis/google/api,\
Mgoogle/protobuf/field_mask.proto=github.com/gogo/protobuf/types:\
$$GOPATH/src \
		proto/example.proto