Sticky keys that are pressed down for longer than
`no-sticky-after-hold-ms` will immediately deactivate upon release. If
the property `no-sticky-after-hold-ms` does not exist, the value of
`release-after-ms` will be used as a fallback.
To combine multiple sticky modifiers, the sticky keys must ignore
other (sticky) modifier keypresses.
This behavior is important for "callum-style mods", where all modifiers
are sticky mods.
Fixes#829
