Support for multiple `.proto` files

[teone]

Hi @emzeq,
and first of all thanks for this tool!

I am trying to generate a graphql schema starting from protobuf, and it works fine as long as the .proto file does not contain any import.

I have a situation similar to this one:

// api/v1/a.proto
import "api/v1/b.proto";
message A {
  repeated b.B foo = 1;
}

// api/v1/b.proto
message B {
  string bar = 1;
}

If I run the compiler on b.proto I get the expected output, if I run it on a.proto I get this message:

proto2graphql --input api/v1/a.proto 
/usr/local/lib/node_modules/proto2graphql/node_modules/protobufjs/src/namespace.js:411
        throw Error("no such Type or Enum '" + path + "' in " + this);
        ^

Error: no such Type or Enum 'b.B' in Type .a.A

Is there any plan to support local imports in the future?

I suspect that it might be something happening in

proto2graphql/src/converter.ts

Lines 11 to 17 in 78b7324

	// Provide resolver for protobuf's well-known types
	root.resolvePath = function(origin, target) {
	if (target.startsWith("google/protobuf/")) {
	return path.join(protosDir, target);
	}
	return defaultResolver(origin, target);
	};

but I'm not very familiar with protobuf in Javascript.