Adzerk-decision-sdk

What's Changed
* Pass API key into explainer request

**Full Changelog**: https://github.com/adzerk/adzerk-decision-sdk-python/compare/1.0.0-beta.14...v1.0.0-beta.15

* Properly marks the repo as Apache 2.0 licensed

Update contentKey to accept type: string

Add API Key to Decision API Call Header for SDK

Add a new option to the impression, click, and event pixels to track gross merchandise value.

Support advertiser Id of each winning ad returned in each decision.