Add posts' featured images

[mnelson4]

It would be a nice option to allow posts featured images to be included in the export. This would probably be another checkmark on the export page (https://drive.google.com/a/eventespresso.com/file/d/1etlOkxOZ6YqdKhIekd0JBevWbSyAAfo-/view?usp=drivesdk).
Thoughts on that? (Again, I'd be willing to put some legwork into making this happen, just looking for guidance or feedback before attempting it)

[boonebgorges]

The main trick here would be making sure that the image is formatted in a reasonable way in each export format. If you wanted to work up a proof-of-concept, this would be the place to start.

[mnelson4]

Hmmm yes, first I'd need to figure out what exactly are all those formats and how they are all currently showing images... but yeah, I'll try to make a proof of concept.

[boonebgorges]

See also #100, #62