Added support for remote Nuget repositories.

[Sumo-MBryant]

The following features and changes have been made:

• API keys may now be specified when pushing to a remote repository
• Symbols may also be pushed
• A few documentation fixes

[stazz]

Thank you @Sumo-MBryant for a nice and clean pr, and also updating documentation!

The missing features were one of those "I don't need them right now, but will add at some point", you beat me to it. 👍

I'll make a new release in a moment.