* Add golint to linters and resolve issues.
I decided to remove constructors for some of the propagation types
because the constructors can be reduced to either using the zero value
or a single, non optional member.
* Enable gofmt and commit fixes
* setup sdk exporter package
* use sdk exporter package in sdk trace
* use sdk exporter package in all exporters
* empty the exporters list before testing Load
* move SpanData to the exporter package
* use the SpanProcessor registration, don't register exporters
* rename exporter structs to avoid stutter
* rename Syncer and Batcher to SpanSyncer and SpanBatcher
So it's explicit they are for spans, and we reduce the risk of name
conflict
* remove not moot todo
* rename sdk exporter to export
* only execute the SpanData if it is sampled
* add batch span processor.
* add blocking support.
* use With* function for options.
- also changed how Shutdown is handled.
* block Shutdown until queue is flushed.
* fix comment.
* 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
This is to shrink the PR #100.
The only place where the registry.Variable type was used was metrics,
so just inline that type into its only user. The use of the
registry.Variable type in core.Key was limited to the Name field.
The stats package also used the registry.Variable type, but seems that
also only the Name field was used and the package is going to be
dropped anyway.
