Python-SDK - 3.1.0

## [3.1.0] - May 3rd, 2019

## New Features:

- Introduced Decision notification listener to be able to record:
- Variation assignments for users activated in an experiment.
- Feature access for users.
- Feature variable value for users.

## Bug Fixes:

- Feature variable APIs now return default variable value when
featureEnabled property is false.

## Deprecated:

- Activate notification listener is deprecated as of this release.
Recommendation is to use the new Decision notification listener.
Activate notification listener will be removed in the next major