More work on assets.
Work on basic menu and tooltip.
Add dozer button.
Add residential button.
Add commercial and industrial buttons.
Fix button hover test.
Add police station and fire station buttons.
Add wire and garden buttons.
Fix button behaviour.
Add hot keys to button specs and select button according to key.
Tweak asset specs.
Add road button.
Fix button hit test.
Add railroads.
Basic behaviour of wire and rail over road is implemented,
but is a big code smell. Needs refactoring.
Add Airport.
Add Coal Plant.
Add Seaport.
Add Stadium.
Update readme.