Make E and Q keys move the camera up and down (as in Unity and UDK).

Make NumPad 1, 3 and 7 select a front, side or top view.  Ctrl-1,
Ctrl-3, and Ctrl-7 select the opposite view (as in Blender).

Alter the mouse-look functionality to prevent gimbal lock when facing
straight up or down.
Document the view keys (Numpad 1, 3, 7) and the ascend/descend keys (E, Q).
Merge remote-tracking branch 'remotes/petex/master'
Restore previous camera yaw + pitch control, but add a toggle in settings dialog to control whether the pitch is clamped between -90 and 90 degrees.
Do not attempt to set a nonexistent default icon.