Add standard tags to Spans?

[pkwarren]

There are some tags which seem like they'd be useful to expose out of the box with the default interceptors, including:

• kind: client/server
• component: grpc-java
• grpc.status: Status.getCode().name()
• error: true (if status.isOk() returns false)

What is your feeling on adding some of these tags to the Spans created by opentracing-grpc? Should this be provided for all consumers (for consistent instrumentation) or added by consumers using the span decorator interfaces?

[malafeev]

I think standard tags should be added for all consumers.
#23 can also be fixed here