Refactor local imports
Rename slot and road as entities
Delete incomplete tiling method
Refactor main driver
Complete unmet test codes
Create layout class
Support interactive road addition
Fix bug: road could be bulit at the outside of world
Fix bug: populate_line function was wrong
Fix bug: pygame was freezed sometimes
Efficient layout building
Update .gitignore for python optimized byte code
Minor change: rename GreedyLayout
Skeleton code for RandomLayout
Implement destructive population
Randomly generate / destruct road network
Change to the road network correctly invalidate slots
Refactor layout code
Merge pull request #2 from elnn/features/road-network

Features/road network