Made the lamp work with ESPHome 2021.10.0

- Fixed transitioning from the off to on state. Thanks to @marcel1988 for informing
  me about his non-functional wake-up light script. Before this fix, the light would
  stay off during the full transformation, only to turn on at the very end.
- The `on_brightness` trigger is now also called at the start of a transition.
  This fixes a problem with the brightness slider illumination not following along
  when you slide your finger over it.
- Suppressing a transition time for transitioning to a night light color is now
  only instant when starting from a night light setting. Before this change, moving
  from for example 80% brightness to 1% brightness (i.e. night light), would be
  instant. Now an actual transformation is done.

* New light transformer implementation
* Fixed missing ; in the code, thanks Jos!
* Removed backward compatibility code for v1.20.x (because there were too many other changes that broke the build, and for which creating a work-around was not feasible).
* Fixed duplicate api section in the example.yaml (thanks @badbroechten\!) and updated the example to not use an underscore in the hostname.
* Prepare for release

* Validate preset names and group names at compile time (fixes #15)

* Small fix for using a less confusing var name.

Co-authored-by: Maurice Makaay <mmakaay1@xs4all.net>

* Implemented compatibility with color mode support in the latest Home Assistant + ESPHome.

* Made the code compile with both v1.20.* and v.1.21.0.

* Made the code compile with both v1.20.* and v.1.21.0.

Co-authored-by: Maurice Makaay <mmakaay1@xs4all.net>

Co-authored-by: Maurice Makaay <mmakaay1@xs4all.net>

* Added OTA progress to the example.yaml.
* Updated the changelog for the ota progress support in the example.yaml.
* Implemented front_panel.set_level action for easier control of the slider LEDs.

* Document the newly found per-LED option of the front panel.
* Implement front panel HAL layer support.
* Implement actions for the output component to be able to control the LEDs.

Compatiblity fix for new coroutine setup in ESPHome.

Co-authored-by: Maurice Makaay <mmakaay1@xs4all.net>

Thanks Jos!

* Updated documentation for 1.18.0 release with external components support.

* Moved example.yaml to the root dir, in line with the recommendations from the ESPHome external components guide.

* Normalized the version numbering for ESPHome references.

* Fixed the styling of the example.yaml references.

Co-authored-by: Maurice Makaay <mmakaay1@xs4all.net>