Cleanup: camera.c

[unofficial-fish]

Changes:

• camera_look_at_point helper function
• camera_update_attract_random is simpler, and includes the internal attract view
• Probably fixed some Dutch angles I've seen on occasion - the roll is being explicitly set to zero where it wasn't before
• more application of vector functions and macros
• camera->update_timer is decremented in camera_update rather than all over the place
• other minor tweaks