Fix modifier plus keypress magic number

After the all_usb_keys merge this now types right modifiers instead of
left modifiers so only works by accident.  Now it types left modifiers
as described in the documentation.
Send composed keys immediately

When a layout combines a modifier with a keypress these may be picked
up together in a single USB keypress.  This may cause, for example,
un-shifted presses to be shifted when they are typed "too fast".