Python's PEP 8 specifies that one shall use spaces instead of tabs as
coding style, and we actually honor that currently. Our EditorConfig
does not special-case Python scripts, though, which is why we end up
with our C coding style and thus with tabs.

Special-case "*.py" files to override that default with spaces to fix
this.

Update editorconfig to match our coding style. Most importantly, we set
up the tab width to be 8 characters instead of the default and use
2 spaces to indent YAML files.

Markdown uses trailing whitespace to indicate context; eg, a blank line
with four spaces indicates that there is a hard break between the
(indented) lines surrounding that line.  Ensure that editors do not
remove this blank.