* Update License header for all source files
- Add Apache 2.0 header to source files that did not have one.
- Update all existing headers dated to 2019 to be 2020
- Remove comma from License header to comply with the Apache 2.0
guidelines.
* Update Copyright notice
Use the standard Copyright notices outlined by the
[CNCF](https://github.com/cncf/foundation/blob/master/copyright-notices.md#copyright-notices)
* Add zipkin exporter
The zipkin exporter implements the SpanBatcher interface. It follows
the current-at-the-time-of-writing document about conversion from
OpenTelemetry span data to Zipkin spans. Which means that endpoint
information is not yet filled.
* Fix typo in docs
* Add a zipkin example
This sends span information to a locally running zipkin collector.
Currently I have a problem getting the collector to show me the spans
after accepting them with HTTP 202. Not sure if this is because of
missing endpoint information.
* Make gitignore consistent
The fixed paths should be prefixed with a slash. The "relative" paths
mean that git will ignore all the files that end with the path.
* Add tests for zipkin exporter
