Added a "flat" mode for environments that makes them follow you around on the
X/Z axes.  The default environment is flat.  Closes #2378.
Merge pull request #2401 from ey6es/flatmosphere

Added a "flat" atmosphere mode (the default) that makes the atmosphere follow you around on the X/Z axes.
Merge pull request #2399 from ey6es/master

Fix for movement being stuck if you switch focus when a key is pressed.
Let's actually use the result of our format conversion.