Add support for segments

[neilenns]

Fixes #61. Fixed #73.

Description of changes

Check for a new seg attribute on the payload and if present use that for all of the segment information that gets passed along to WLED. If it isn't present then the node behaves like it used to.

Checklist

If your change touches anything under src or the README.md file these items must be done:

• [X] User-facing change description added to unreleased section of CHANGELOG.md

[neilenns]

@daredoes since you recently touched this code it gave me this idea for how to actually support segments via the incoming payload. Would you mind taking a peek and see if you agree with my logic here?

[neilenns]

Thank you! Merged and released as v2.2.0.