* Temporarily opt-out export.Labels from label encoding stuff
* Stop passing label encoding stuff to export.Labels
* Drop label encoding stuff from SDK
* Dogstatd exporter does not need to implement label exporter anymore
* more dogstatd exporter fixes
* export labels get back to encoding stuff
in a lame way, but improvements are coming in following commits
* Get encoded labels through export.Labels
* make SDK to provide its own implementation of export.Labels
* drop dead code
* add noop label exporter
* make export simple labels immutable
* Move the default label encoder to export package
* Simplify the simple export labels a bit
* Reserve some label exporter IDs
* Document and shuffle the code a bit
* Prepare for bring the iterator benchmark test back
We can install a callback to the Batcher's process function - this is
the place where we can access the labels, and thus test the label
iterator.
* Bring back the iterator benchmarks
* Simplifications and docs
* Fix copyright to be consistent with the rest
* Fix typo
* Put reserved label encoder IDs into constants
We get fewer comments about magic numbers that way.
* Fix the label encoder as label exporter thinko
