Remove guage & add Observer metric instrument#498

Merged

SergeyKanzhelev merged 7 commits intoopen-telemetry:masterfrom MikeGoldsmith:remove-guage

Feb 26, 2020

+288-298

Commits on Feb 18, 2020

Commits on Feb 20, 2020

Commits on Feb 25, 2020

fix metric tests
MikeGoldsmith
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Commits on Feb 26, 2020