v0.4.0

Another small update:

• Rebalanced bots a bit - less Void effects from bots.
• Added card "Trenches" - it adds fortification to all fields with buildings
• Added card "Discount" - it makes a random card in deck permanently cheaper to play  
  
• Added card "Bulldozer" - it fires bullet with power 50 but piercing 2 (so it's good for very fortified fields, but can conquer max 2 fields)
• Rebalanced cards a bit,  like usually