ToggleTaskbar

Toggles the "Automatically hide the taskbar" setting and optionally hides it completely.

Usage

build or download TaskbarToggle.exe
create a shortcut in your start menu and give it a Shortcut key, e.g.:
add the -x argument to completely hide the taskbar
to override toggling, you can use -v to always show or -h to always hide

Troubleshooting

hiding only works when launched via Shortcut key (it assumes it's launched within the same process)
if the Shortcut key lags about 3 seconds, disabling "Let apps run in the background" usually fixes it (see this answer for more..)