Subtract min sensor value per slider

[douglasbakkum]

This improves touch position accuracy in noisy setups.

Touch position is calculated with a weighted average of the sensor readings. If properly calibrated, sensors on the opposite end of a finger touch would be zero and thus make no contribution to the weighted average. If the baseline sensor readings are elevated, the sensors on the opposite edge do contribute to the weighted average, making a positional artifact (i.e. the position is more central than it should be in reality). This artifact is higher when the finger is a bit distant while approaching and lower/negligible when the finger is fully touching the device. This can cause the position to move enough to enter "slide" mode and disable "tap" events being emitted.

[benma]

@douglasbakkum to format the code (fix the CI issue), run ./scripts/docker_exec.sh ./scripts/format outside dockerdev or ./scripts/format inside dockerdev.

[benma]

@douglasbakkum please add an entry to CHANGELOG.md :smile:

[douglasbakkum]

@benma 👍 added

[douglasbakkum]

ack. happy for the nit and explanation. now squashed and pushed