Made the lamp work with ESPHome 2021.10.0

* 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

* 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>

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

Implemented support for presets.