Update 2:
The game was updated again, to add a message about how to quick switch weapons. Also there is an additional note to help guide players later in the game, and the jumping spider enemy behavior changed.

Update 1:
Y - Axis invert is now an option in the General settings section of the in-game Pause Menu.

This will be set by default to on when you launch the first time after the update so toggle it off if you do not want an inverted Y axis.