Previously, we used index-ordering for layers, meaning, we looked keys up based
on the index of active layers. This turned out to be confusing, and in many
cases, limiting, since we couldn't easily shift to a lower layer from a higher
one. As such, index-ordering required careful planning of one's layers, and a
deeper understanding of the system.
This patch switches us to activation-ordering: the layer subsystem now keeps
track of the order in which layers are activated, and uses that order to look
keys up, instead of the index of layers. This makes it easier to understand how
the system works, and allows us to shift to lower layers too.
It does require a bit more resources, since we can't just store a bitmap of
active layers, but need 32 bytes to store the order. We still keep the bitmap,
to make `Layer.isActive()` fast: looking up a bit in the bitmap is more
efficient than walking the active layer array, and this function is often used
in cases where speed matters.
As a side effect of the switch, a number of methods were deprecated, and similar
ones with more appropriate names were introduced. See the updated `UPGRADING.md`
document for more details.
Plugins that used the deprecated methods were updated to use the new ones.
Fixes#857.
Signed-off-by: Gergely Nagy <algernon@keyboard.io>
Gergely Nagy