Rework modbus documentation.

[janiversen]

Proposed change

The modbus documentation had become a bit "clouded" and information was not logically grouped. This PR tries to make a more logical view of how the configuration works, as well as making it easier to use the index.

It is based on next instead of current, due to the pending changes (2021.6) which are on next.

This also contains the documentation for the new Fan and Light platforms.

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logo's and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

I am not a native English speaker so suggestions to correct the wording will be accepted immediately.

Incorporates #15329, which are closed.
Incorporates #17207, which are closed.

• Link to parent pull request in the codebase:
  Add Modbus light integration core#42120
  Add Modbus fan integration core#48558

• Link to parent pull request in the Brands repository:

• This PR fixes or closes issue:

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

[janiversen]

It tells me line 8 is wrong, but I did not touch the first lines at all, I am confused.

[janiversen]

@frenck Can I politely ask for advice...the build tell I have an error in line#8 column 284. But the commit does not touch line 8 (first line touched is 21, and that looks ok to me). Can you give a hint where/how to search for the problem ?

thanks in advance.

[janiversen]

How super to see the site in a PR. This PR is ready from my side.

[janiversen]

Do I miss to do something (it is no good idea, that I approve my own work) ? Code is coming in 2021.6 so I hope this doc. will as well.

Comment addressed.