Closes #90

clarify form/bao role

Fixes #79

per comments from @eileen here https://github.com/civicrm/api4/issues/14#issuecomment-278860730

mkdocs.yml - Rearrange top level of TOC

fixes #84

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).

More hook fixes

extend-stages - clarifying intro paragraph

Hook fixes for L, M, N, and O

Conflicts:
	mkdocs.yml

This completes the migration of all hooks pages to close #71
and also sets the theme to Material

Conflicts:
	redirects/wiki-crmdoc.txt