Auto updater/update checker!

[nkomarn]

So, I am on an ongoing mission to create some sort of update feature for Harbor. Idealy, I would want the plugin to somehow automatically update, but I heard that that might be against Spigot's TOS, so I am not sure. If that isn't possible, I want to try to make at least an update notifier (which could be disabled, of course). I don't really know how to go about either though- I've googled about to find a solution and most no longer work so that's a shame. Anyways, any help would be appreciated! :D