Adds keyboard shortcuts for adding the currently-held item to the toolbar:
CONTROL + Q: Assign to first open slot.
CONTROL + [0-9]: Assign to corresponding slot. Without a held item, unassign that slot.
NOTE: Due to a bug in the Lua API, the CONTROL + Q shortcut will overwrite any blueprints. See also: https://forums.factorio.com/viewtopic.php?f=7&t=66002
0.3.0: Update for game version 0.17.12 (see also 66142)
0.2.0: Initial working version.