1.3.1 - New Achievement + Fixes

Hey everyone! Today I uploaded a quick little patch to address a few lingering issues after the Workshop Update.

• Added a new achievement! Speed of Light - Hyper jump across a level
  
• Fixed a crash when placing Mud on a bottom row of a level in the editor
  
• Modding in new archers or co-op towers by hand, rather than replacing the already-existing ones, should no longer crash the game
  

Thanks, and have fun!