Release for v0.7.7

[lzchen]

Minor release. Consists of mostly azure related changes.

Trace span attribute changes: [#827]
Log Exporter custom dimension API changes: [#837]
Local storage + retry for metrics exporter: [#845]
Fixed rate sampling for log exporter: [#848]
Telemetry processors for exporters: [#851]

[c24t]

Do we need to update the minimum required opencensus version for opencensus-ext-httplib and opencensus-ext-requests?

Look good otherwise.

[c24t]

Suggested change

	Released 2020-02-03
	Released 2020-02-03

[c24t]

Suggested change

	- Update `azure` module
	- Updated `azure` module

To be consistent with the others

[lzchen]

Do we need to update the minimum required opencensus version for opencensus-ext-httplib and opencensus-ext-requests?

Look good otherwise.

@c24t
Correct if if I'm wrong, but don't we need to update the minimum required version of opencensus only if there were new changes in opencensus that opencensus-ext-httplib and opencensus-ext-requests would rely on?

[c24t]

You're right, I see that these changes just add some new span attributes in the ext packages.

You might want to change the message in the changelog though. "Support span attribute changes in opencensus>=0.7.7" makes it sound like the ext libraries were changed to support attribute changes in the core library.