Epicstore-api

* Slight changes in docstrings for more readability.
* Updated get_offers_data and offers query.

Added new functions to interact with the store.

* get_addons_by_namespace - To fetch games' addons.

* fetch_media & fetch_multiple_media_files - To fetch games' media files.

* get_product_reviews - To fetch games' reviews (if exists).

- Added a new function "get_free_games".
- Fixed an exception in "get_store" method.