Added + and - before radius as an optional char

This allows players to perform time based, vote based or donation based commands to increase the map size.
Examples:
1) Player votes, increase the map by 1 block
2) Player joins (more players) increase the map, Player is offline for X days decrease the map
3) Reached donation goal, increase the map
Merge pull request #36 from Maximvdw/patch-1

Added + and - before radius as an optional char