Add a Makefile to generate gRPC files (coinbase#5)

* Add a rake task to generate GRPC files.

* Switch to a Makefile.

Based on snippets from proto/Makefile.

Author: Rob Holland

Makefile

@@ -0,0 +1,9 @@
+PROTO_ROOT := proto/temporal
+PROTO_FILES = $(shell find $(PROTO_ROOT) -name "*.proto")
+PROTO_DIRS = $(sort $(dir $(PROTO_FILES)))
+PROTO_OUT := lib/gen
+
+proto:
+	$(foreach PROTO_DIR,$(PROTO_DIRS),bundle exec grpc_tools_ruby_protoc -Iproto --ruby_out=$(PROTO_OUT) --grpc_out=$(PROTO_OUT) $(PROTO_DIR)*.proto;)
+
+.PHONY: proto