Support for GitHub Releases

[Arthri]

Description

Please add support for downloading files from GitHub releases(i.e. download Paket 6.0.7's files). I figured since downloading from Gists is already possible, downloading files from GitHub releases can be added too.

Repro steps

N/A

Expected behavior

A similar syntax to adding gist dependencies

Actual behavior

Not implemented

Known workarounds

Use HTTP dependencies, although they don't work for private repositories

Thanks for the amazing project btw!