New minecraft version. (1.15)

[xoft]

We still do multi-protocol support, and we try to support as low as possible, but those old versions were too different and supporting them was becoming too much of a burden. It was holding us back too much, so we decided to drop the oldest protocols. They were too buggy anyway.

I don't plan on dropping the 1.7 protocol any time soon, we'll try to keep the server compatible for as long as possible again. Mojang has become somewhat conservative in their protocol changes so it's easier to support multiple versions nowadays.