GRIDROAD v1.04 - AI tweaks and WASD road marking placement — GRIDROAD Steam update #1554958

Changelog - Tweaked the car AI. Throughout the game's development I've been caught between two crowds. One crowd wants cars to behave realistically and not crash, the other likes a more arcadey AI that can be exploited to produce very visually pleasing but very unrealistic solutions to levels. I've tweaked things so that hopefully both crowds will still be happy. Cars now spawn with a regular cadence and also the drivers will be less careful when pulling out into junctions. This will mean your existing solution will give different scores but the score ceiling for nearly every level should be higher. - Added WASD road marking placement controls. If you press a WASD key over a tile you will add/remove that direction of arrow to the tile. Merge markings can be placed by holding the "backwards direction" WASD key and then pressing another "side" key depending which side you want the merge on...