Pyramid-mixpanel

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* Include py.typed in the package, third time is the charm?
[zupo]

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* Include py.typed in the package, now for real.
[zupo]

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* Include py.typed in the package.
[zupo]

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* Prepare for PYPI release of the rewrite.
[zupo]

* Small performance optimization.
[zupo]

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* Add guards that make sure parameters sent to MixpanelTrack are valid.
[zupo]

* Don't flood logs with "mixpanel configured" messages.
[zupo]

* Support for the `people_append` method.
[suryasr007]

* Lots of cleanup of legacy assumptions:
* `profile_sync` method was removed
* request.user no longer required
* MixpanelTrack init now accepts `distinct_id` instead of `user`
* `state` ProfileProperty no longer required
[zupo]

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* Not all consumers have a .flush() method.
[zupo]