GitLab

* Migrate relevant documentation from arduino/Arduino wiki

* Trim trailing whitespace

* Add newline to end of file

* Increase heading levels so that the minimum level is h2

This is required for table of contents generation.

* Use supported line break markup

The backslash at end of line to cause line break is not supported by the documentation build system.

* Update links to migrated pages

* Fix list markup

The documentation build system requires a blank line before the start of a list