* 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.
Damien Mathieu
rghetia