(GH-86) add request for debug output
(GH-106) reimplement mailsender with markdown options set

This allows emails to be more plaintext with mailsender converting links and
other things inside the message.
(GH-106) plaintext emails should limit markdown

With markdown options automatically converting urls, we don't need to set them
up with markdown now.
(maint) prep for release of plaintext email enhancement

(GH-106)