Fix problem where the player can't clear the last road they built.
Fix strange behaviour when the player clicks and drags outside the play area.
Merge pull request #3 from djcsdy/drag-out-of-bounds-upstream

Fix strange behaviour when the player clicks and drags outside the play area
Merge pull request #2 from djcsdy/click-twice-upstream

Fix problem where the player can't clear the last road they built.
Add pathfinding and make buses move between bus stops.
Fix bug: sort by lowest cost rather than highest!
Make buses turn
Make buses wait at stops
Make map larger and allow scrolling around with arrow keys