Here's another bunch of changes going by the name 0.7!

New features

• Added new poison tower that does damage over time.
• New turret upgrade window.
• Turret upgrade options for slowing tower and bomb tower.
• Turrets can be sold.
• 20% buy/sell penalty for turrets bought/sold when a wave is in-progress.

Fixes

• Turret range is shown when turret info box is open.
• Difficulty level persists when going back to the lobby

Balancing

• Basic turrets now fire further.
• Bomb turrets now fire a shorter distance but do more damage.
• Upgrade costs increased.
• Difficulty levels changed to -50%, 100%, 200% and 300%