Validate some common errors in links.

Show error messages when editors put in non-absolute links, hover text, or rel=external in their markdown.

https://www.agileplannerapp.com/boards/173808/cards/3357
Is this correct?  As I understand it, the guidance for title attributes in links was to set them when the title of the destination document isn't obvious from the link text.  This is to make things easier for screen-readers.