typo fix

There was a missing trailing underscore (`_`) that would have marked the
content in the backticks as a link. This adds it and fixes the link on
every core module page.

Modules are almost always written now by mutliple authors, so don't show this field on website, since it grows obsolete and does not take into account all contributors.
Contributors are still listed on github module source and in repo, and original authors still in the file for when development questions arise, but want
to funnel support questions to the mailing list versus directly to them.

Rename "jpfunc" to something more explanatory

- The html_ify filter now escapes HTML found in module documentation.
  THIS COULD AFFECT MORE THAN JUST MARKDOWN but I didn't see any modules
  expecting to use e.g. HTML entities or HTML tags in their
  documentation.

- The markdown_ify filter (used as jpfunc in markdown.j2) escapes at
  least a few Markdown in-line formatting characters.

- Improvements to markdown.j2:

    - Call jpfunc on the module name heading so that it gets escaped for
      Markdown (e.g. my_module_name becomes my\_module\_name).

    - Added paragraph breaks between paragraphs in the description.

    - Added examples heading, which is consistent with the notes heading
      below it.

tweak position & look of Requirements in rst
tweak APT's notes as per anhj's wish

return DOC and EXAMPLES as a list
add moduledev explanation
more

At the moment Ansible prefers yes/no for module booleans, however booleans in playbooks are still using True/False, rather than yes/no. This changes modifies boolean uses in playbooks (and man pages) to favor yes/no rather than True/False.

This change includes:

- Adaptation of documentation and examples to favor yes/no
- Modification to manpage output to favor yes/no (the docsite output already favors yes/no)

 Add HTML-escaping to code examples in rST tempate of module-formatter
 Add support for specifying port, addresses with phrases and attaching files
 Add support for custom headers and document version_added for new options
 X-Mailer header added :)
 protect empty address lists & attachment list, and add bcc

   ongoing work for the Booklet

 - fixed template (it was the template), adding indentation with Jinja2
 - added description of code examples to man-page template (was missing)
 - fixed fireball, cron, and debug module examples to confrom

- Uses HTML tables and Github-flavored code blocks (3 backticks)

- Updated man template accordingly
- seem to have left in illegal char in facter DOCUMENTATION...