Output features, crop and audio asset effects (includes breaking changes)

This update adds API access to the the following features to the SDK:

Crop and image or video asset
Add volume effects to audio asset
Add 4:5 aspect ratio
Render a range (portion) of a video
Select a frame rate for the video render
Render an mp3 audio file (no video)

It also updates to use the latest OpenAPI generator version 5 which requires PHP 7.2. This will be a breaking change to anyone using PHP 5 or 7.1.

shotstack / shotstack-sdk-php

Output features, crop and audio asset effects (includes breaking changes) #8