We need to store the previous state of the keys, to figure out when a specific
key is released, as opposed to simply not being pressed. This is required for
layer keys such as `Mod` and `Fn` to work properly when there are more than one
of them on the keymap.
Without being able to tell when a key is released, we would not be able to turn
a layer off only when no layer key is held. Not easily, anyway: we'd have to
track the state of all layer keys... but then it is easier to just track them
all.
Thankfully, the memcpy at the end is fast, as it only needs to copy 70 bytes.
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
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