cleanup nuget and add support for pre-release
Merge remote-tracking branch 'yolodev/feature-nuget-pre'

Conflicts:
	server.js
Omit needless spaces and logs.
Added text for anonymous receivers on Gratipay
Support Pub package manager for Dart

Fixes #278
Pub example.

Closes #279
Website: codecov, hackage, pub, nuget/myget