* Support instrumentation library in metrics
* Update stdout exporter to display instrumentation info
* Fix tests that use the STDOUT exporter
* Refactor to keep SDK out of API
* Update global Meter and test Meter version
* Revert unneeded import syntax change
* Fix Unit comment
* Update comments
* Update comment
* Revert no-op change to import
* Refactor api.go
* Refactor more
* Finish
* More
* Rename
* More rename
* Split observer.go common into async.go; rename common.go sync.go
* Move types a bit