Add documentation for Control class (issue #2150)

[mosessamofficial-sys]

Adds documentation for the Control class, including examples of built-in controls and wiring custom Leaflet plugin controls.

Closes #2150

[mosessamofficial-sys]

Hi, this is my first contribution.
Please let me know if any changes are required.

[hansthen]

Looks good to me. There were some formatting issues, which I can fix if you want. If you want to contribute more frequently, you may want to setup our commit hooks framework. This will automate a lot of the basic checks.

[hansthen]

There is a small issue. You used a Dummy example L.Control.MyPlugin. Because of that our automated tests fail. Can you rewrite the issue using a simple real world example?

[mosessamofficial-sys]

Thanks for the review! I’ll update the example to use a real-world Leaflet control so the automated tests pass.

[mosessamofficial-sys]

why its always failing , i don't understand.