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This also refactors the fixed level table which is now a list of indexes
in the normal ramping table. This saves some memory because we have less
computations later.

Also ramping_up is now just signed ramp_direction.

We also consistently ramp into the direction of the initial brightness
(more or less, you'll see).

This allows changing the ramp value in short intervals.

This makes everything a bit more consistent.

It doesn't make lot of sense as it is not much lower than the normal
low, but requires 14 bytes of flash. It also conflicted with the strobe
mode. A similar mode can be achieved by setting "start on low".