creep spawning is now defined in waves in the mission.inis; each wave creates new spawn points, these could in theory be at any position on the map; a delay at the beginning of each wave is set in the mission.ini but is not yet implemented.
Rebalancing the game will be necessary now as later waves can easily be fought off with the infrastructure built during the first wave.
Merge branch 'develop' into origin/feature/issue/#63
missing commas
slightly modified difficulty setting