Gracefully handle errors in model loading. Fixes NetLogo/LevelSpace#138
Preserve original file path in compiler error messages
Disable generator for child models, dramatically speeding up model load times and reducing memory consumption. Fixes NetLogo/LevelSpace#59 and NetLogo/LevelSpace#120.
Made headless models use normal repaint mechanism, meaning they now work with display and repaint significantly less. Fixes NetLogo/LevelSpace#94
Hidden interactive models now run at full speed. Fixes NetLogo/LevelSpace#125 and NetLogo/LevelSpace#136
displayand repaint significantly less. Fixes NetLogo/LevelSpace#94