"Security Doucmentation" --> "Security Documentation"

Minor corrections.

The most canonical form is to present entities in camel-case and and to
present actions in lower-case.  This matches the API explorer.

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

The `first_name`/`organiztion_name` is kind of an ugly bit and tangential to
the main point here (entities vs actions vs parameters).  Choose fields that
more clearly apply to all contacts.