Initial public alpha release

Initial public alpha release of the SpellMaster plugin.

• Contains a good selection of tomes and spells (more are planned).
• Testing has been very limited for dealing with multiple players and casting spells in the Nether and End dimensions.
• Debugging commands and log messages are still present.
• Compatibility with future plugin releases not guaranteed (player may have to reacquire tomes once a plugin upgrade is done)