Updates the changes as suggested by Mikey

Co-Authored-By: Mikey O'Toole <mikey@mjco.uk>

based on https://chat.civicrm.org/civicrm/pl/etog75icwjywt84sxtw11fumoh

Close #86

perl -0777 -i -pe 's|^(.*)\n-{3,}$|## $1|gm' `find . -name '*.md'`
perl -0777 -i -pe 's|^(.*)\n={3,}$|# $1|gm' `find . -name '*.md'`

Large scale clean up of markdown code (in almost all files) to conform to markdown conventions that I observed to be used consistently in the official CiviCRM User Guide. These convensions are now documented in the markdownrules.md file