Rustfmt

Added a basic rustfmt config.

I noticed you use Visual Indetion and preserved it.

the config over all does the following:

• 4 spaces indetation
• Spaces over tabs
• Max width 100
• Comment width 100
• Wraps long comments
• Unix like \n newlines
• formats strings if they overflow. So "f..ooo bar" becomes "f..ooo \\nbar" I think.
• Reorders imports, imported names, and imports in groups

If rustfmt is fine, I can follow up with a CI config