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

tweaks

Misc > Markdown: removing TOC from page content b/c it's already available in nav menu, and including it in page content does not seem consistent with any content in user guide

gender-inclusive pronoun for extension devs

During the meeting of the Extension Working group on 27-Oct-16, we discussed
trade-offs in the names.  (Ex: Now that "Stewardship" has an option for
"Seeking Maintainer", it seems a bit confusing to have "Maturity" as
"Maintained/Unmaintained".) There was support changing these two names and
no opposition.

The goal is to publicize this soon in a public blog.  Hopefully, this is the
last round, but if there's strong feedback we could revise again.

extend-stages.md - Fix table layout in Github

The table layout looks right with `mkdocs` but not with Github. This works in both.

Add "Extension Lifecycle" chapter

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.

Assorted documentation improvements.

Made TODO one word again.

Added link to Wiki so we can link to these docs rather than the wiki for the civicrm.org downloads page.