1.4 - just touchups but breaking

This update renames cleans up a few things:

• The annotations were moved into their own package (bukkit, bungee, velocity).
• @Plugin got renamed to @BukkitPlugin to reflect the name prefix of BungeePlugin and VelocityPlugin.
• The version property was removed from the annotations to avoid confusion - providing one via build system is required anyway.
• The readme was cleaned up and mostly moved into wiki with long overdue updates.

As usual, it's already up on jitpack