* Update Tracer API with instrumentation version
Add option to the `Provider.Tracer` method to specify the
instrumentation version.
Update the global, noop, opentracing bridge, and default SDK
implementations.
This does not propagate the instrumentation library version to the
exported span. That is left for a follow-on PR.
* Revert trace_test.go
This is for the next PR.
* Update SDK to include version for default instrumentation
If the instrumentation library name is empty and the default
instrumentation is uses, include the SDK version.
* Update comments and documentation
* Remove default instrumentation version
