Consider aligning API w/ Bazel proto idioms

[perezd]

Hey there, I was reviewing this example and I notice your example could be more idiomatic with existing Bazel proto rules.

1. <lang>_proto_library should prefer to use depson a proto_library vs referring to it as a src. Example can be found here: https://docs.bazel.build/versions/master/be/java.html#java_proto_library. The rationale being this is generating source code from a collection of dependencies and is usually expressed that way.

2. ts_library targets that wish to use the generated ts lang proto library should express dependency on the target using deps instead of src. It's considered generally a best practice to declare a label in srcs that is directly are directly consumed by the rule that output source files (citation). In this particular case, I believe the ts_library is depending on a previously generated target and wouldn't be expected to list it as a src of the library itself. Additionally, its considered a best practice to not have the same file listed in srcs of multiple targets, which this would cause.

[thesayyn]

Hey, I agree with the first one that says _proto_library should definitely pick up the descriptors from "deps" attribute instead of "srcs".

Since _proto_library is a source generating target, we should not think it as a JS-producing target and also I'm not sure if ts_library picks up source files from the "deps" attribute. (I guess I'm gonna see if it works that way.)

[thesayyn]

Fixed in 0.0.7