v.1.2 comes with major bugfixes
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+ fixed some spectator bugs
+ double jump is now independent of the pitch of a player (facing up or down)
+ remade the scoreboard
+ no flickering on the scoreboard
- removed unnecessary class "ScoreboardManager" (this was featured by mistake in v.1.1, now removed)
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I'm still considering remaking the whole plugin (cause the code is partially completly outdated) with API and publishing open-source, but only if there's enough interest there...