Added a configuration!

Fixed:
A few bugs.

Working on:
Customisable Messages with a config.yml

Basic 1.2

Added
A custom join message
A custom leave message

Update 1.3

Added 1 new gamemode

Working on 1 new gamemonde

Completed:

Adventure mode:
Command: /gma
Permission: basic.adventure

In progress:

Spectator mode:
Command: /gmsp
Permission: basic.spectator