Managed to add quite a significant feature - part rotation! Now you can get even more creative with your vehicle designs!

Also added in this update:

• Part solidity - you can no longer connect parts to the tyres of the wheel parts as they are considered non-solid.
• Non-solid parts are represented with slightly darker borders when selected.
• An arrow to show the current rotation.
• A couple of extra tutorial dialogs.
• Spruced up the main menu a bit.
• Various bugfixes.

You can check the source for more details.