[feature request]There is no API for [ Get a single release asset ]

https://developer.github.com/v3/repos/releases/#get-a-single-release-asset
I think it is very important to wrapper this API

for example, I am dealing with the auto-update of electron. I am trying to let the client-side to detect the latest release by itself and download the release asset to update.

Start by reviewing the repository's existing release-related API wrappers and compare them with the linked GitHub endpoint for getting a single release asset. Done means the wrapper exposes that endpoint and supports the Electron update use case described in the issue.

索引モデルが issue の本文から書いたものです。