Closes #90

This is for people who are writing code.  It would be great if all of them
also wrote docs, but...  a new dev should learn a bit about dev before they
start contributing to dev-docs.  ;)

(I appreciate "Documentation Driven Design" but not "Doc first, ask questions later".)

The menu sets up divisions between "Core/Extension" (which are similar but
different -- two styles of packaging and collaboration) and "API/Hooks"
(which are similar but different -- two types of interfaces).

that URL hacking works

(I looked at the content in this file to make sure there's nothing in it
that can't be found elsewhere. All content already exists in the wiki
and thus is moved over as part of auto migration for hooks.)

(files still need to be moved around)

https://pythonhosted.org/Markdown/extensions/attr_list.html

https://wiki.civicrm.org/confluence/display/CRMDOC/Debugging+for+developers

https://wiki.civicrm.org/confluence/display/CRMDOC/Before+you+start

Original here:
https://wiki.civicrm.org/confluence/display/CRMDOC/Create+a+Module+Extension

still missing some macro content! :-/