Add better camera controls

[amterp]

Stretch goals.

The spec only specifies the camera to:

• Allows mouse pitching/yawing.
• Movement with WASD.
• Not be weird with the ground.
• Start at a sensible perspective.

We can add to this. Things to potentially add:

• Camera rolling with Q/E.
• Going 5 - 10x faster when holding shift i.e. "sprinting".

[amterp]

Sprinting has been added as of #35. Rolling may still be implemented.