Optimizely-sdk

* Updated datafile parsing to be able to handle additional fields.
* Deprecated Classic project support.

* Included datafile revision information in log events.
* Added event tags to track API to allow users to pass in event metadata.
* Deprecated the `event_value` parameter from the track method. Should use `event_tags` to pass in event value instead.
* Updated event logging endpoint to logx.optimizely.com.

* Introduced support for Full Stack projects in Optimizely X. No breaking changes from previous version.
* Introduced more graceful exception handling in instantiation and core methods.
* Updated whitelisting to precede audience matching.

* Added support for v2 endpoint and datafile.
* Updated dispatch_event to consume an Event object instead of url and params. The Event object comprises of four properties: url (string representing URL to dispatch event to), params (dict representing the params to be set for the event), http_verb (one of 'GET' or 'POST') and headers (header values to be sent along).
* Fixed issue with tracking events for experiments in groups.

* Updated requirements file.

* Introduced option to skip JSON schema validation.