Update Notes for v0.99

Added a new built-in campaign: Race Challenges
Added 11 more built-in circuits (with AI lines for all four built-in vehicles)
Added achievements (there are now 46 achivements to gain in various ways)
Added experience system - play any game modes to gain experience
Added rank system - advance in Race Challenges and Time Trials and gain enough experience to get promoted to new ranks
Added Progress Menu to see information about your stats, achievements and rank
The old Beta Race Campaign can still be opened by holding Shift and Ctrl when opening Race Challenges
Level Editor: Fixed level preview sometimes having slightly wrong colors
Level Editor: When changing the selected road marker or checkpoint, remembering which property folders were open
Level Editor: Added some more grass textures
Level Editor: Fixed a minor Z-fight flicker issue in pit templates
Gamepad thumbstick buttons to change the stats submodes are now disabled by default (to prevent accidental mode changes)
AI Editor: Level can now be changed after testing or training, too
AI Editor: Added a button to show info about all recordings in the current collection
AI players of different skill levels/groups are now blended better (smaller gaps between the levels)
Host: Automatic vehicle selection now works better with voting (and also disabled if there is not one fixed vehicle)
Fixed some HUD elements sometimes overlapping in an ugly way in the split-screen mode
Added new parts to the menu music
Miscellaneous other minor fixes and improvements