Unfortunately, the popular Markdown editors (VS Code and Typora) still
don't support the more human-friendly TOML front matter syntax.
Therefore, make it easier to edit content in popular editors by
converting the demo front matter from TOML to YAML.
Except for publications as they are primarily data based (rather than
content based) and are automatically generated by Academic Admin.
Also, continue to use TOML for configuration files.
See #1069
* check if the Hugo generated author profile URL is valid
* works around the Hugo bug, preventing invalid links
* rename `author` folder to `authors`
* no need to GetPage authors/x and then GetPage author/x to check if
user account was created
* can just rename the folder and use `if .File` instead
* more aligned with how Hugo's taxonomy system was designed
* refactor all author code
BREAKING CHANGE: rename `author` folder to `authors`
Fix#1064
George Cushen