Since these methods are about the span itself rather than specifically
*events* on the span, it makes sense to drop "events" from their names.
[Closes#33]
* rename finish -> end
* missed a few finish -> end spots
* change end back to finish for the bridge span in the openTracing bridge
* fixed grammar, ran make
* Allow specifying custom timestamps for events
Adding event with timestamp is not yet a part of the OpenTelemetry
specification, but this function will come in handy when implementing
the OpenTracing bridge.
* Add opentracing bridge, wrapper tracer and migration interfaces
There are some features missing - setting up links and span kind;
context propagation will only work between two OpenTracing bridges.
* Add some tests for the opentracing bridge
The tests mostly check various aspects of the cooperation between
OpenTracing and OpenTelemetry APIs.
* Merge two event methods in span API
There was an agreement to get rid of the Event interface and
consolidate the two methods for adding events into one. See #57.
* Eliminate the use of the Event interface
There is no need for the SDK to provide the implementation of the
Event interface - it is used nowhere.
* Drop the Event interface
It's dead code now.
* Make it possible to override a finish timestamp through options
Opentracing to opentelemetry bridge will certainly use this feature.
* Obey the start time option
* Add tests for events and custom start/end times
* add tests for api/trace/current.go
* add interface validaion for type: mockSpan
* rework for exported NoopSpan and ditch useless tabletest for TestSetCurrentSpan()
