Additional event/channel data types (relative, timecode, strings, etc)

[cbdevnet]

Some backends, notably the evdev and maweb backends have controls that output relative values instead of absolute values.

For the evdev backend, these are currently mapped into absolute values using a configuration-provided range value.

There might be value in introducing relative channels as another type of channel, which can be mapped from other relative channels and deltas of absolute channels. Mappings from relative channels to absolute channels would need to either be specified with a range or just be disallowed.

[cbdevnet]

As an additional idea, some backends have the notion of time-code channels (MIDI, maweb and OSC all have provisions for this in some form). This would require an additional channel type.

[cbdevnet]

This has additional implications on configuration file format and presentation, as information on why channels with differing types may not be translated into eachother needs to be presented clearly to avoid confusion.