Check for compatible updates in plugin

[boatbomber]

Adds opt-in settings for checking for updates. This should hopefully reduce the number of reports we get from people simply using outdated versions.

It will not notify about major version updates, since those are potentially breaking and the user may have reason to remain on the older version.

[Dekkonot]

I'm of two minds here.

The first loves this because it'd serve as a reminder for people to actually update their dang Rojo releases.

The second thinks this'll be annoying and that prompting people for pre-releases might be a problem since we don't plan to publish the plugin to the website for those versions. I appreciate how you can turn it off but I'm not sure how much I like a feature that my first thought was "I hope you can turn it off" for.

[boatbomber]

You're correct in that prereleases are likely to cause more confusion for marketplace users... Should I disable that subsetting when installed via marketplace? I can detect that pretty easily.

[boatbomber]

If you install Rojo via marketplace, the Include Prerelease setting is hidden to avoid confusion.