File reference pages

This commit includes changes to the infrastructure files
and a draft of the "Intro" page for the doc plus some skeletal
pages for review.  It also includes a README.md file with
instructions for creating a new page and template files that
can be copied to begin a new page.

See https://blueprints.launchpad.net/fuel/+spec/config-file-reference
for more information.

Change-Id: I660ddc28acb4da70e62a5cfe85ec91d0e213c07d