API Documentation found here:
https://developer.github.com/v3/repos/releases/#list-assets-for-a-release
https://developer.github.com/v3/repos/releases/#upload-a-release-asset
https://developer.github.com/v3/repos/releases/#get-a-single-release-asset
https://developer.github.com/v3/repos/releases/#edit-a-release-asset
https://developer.github.com/v3/repos/releases/#delete-a-release-asset

I've created the following PR with the APIs added in:
#525