Pass proto root and proto file to grpc.load

[zachgrayio]

I made a small change to pass proto root and proto file to grpc.load(), allowing for correct inclusion of additional protobuf files.

The interface becomes the following:

export declare function clientFactory<T>(protoFile: string, protoRoot: string, packageName: string): ClientFactoryConstructor<T>;

This allows us to do something like this in our service definitions, assuming that the imported proto files are available in the path provided when calling the above function:

import "google/api/annotations.proto";
...
  rpc Echo(StringMessage) returns (StringMessage) {
        option (google.api.http) = {
            post: "/user/echo"
            body: "*"
        };
  }

Unfortunately this isn't the cleanest pull request - I haven't had a chance to get the tests working because I can't seem to get them running on my machine. I also had to use Node v7.10.1 and NPM v4.2.0 and make some tweaks to package.json to get the thing building (there was a yarn.lock but not package-json.lock in master).

Getting this fork to a mergeable state shouldn't require much more effort, but I don't want to spend much time on it if there's not any interest in merging it.

[zachgrayio]

it seems this requires a few more changes to function properly but we're actively working on it, will update PR with details soon.

update: this is working great for our use case, but we still need to do some work to get the tests updated and passing.