Regroups documents into 3 sets::
1) Documents needed when first encountering Zephyr. (Basically what
you need to decide if you're interested in Zephyr, what it can do
for you, and how to get the code so you can experiment with it.)
2) Documents used when developing new Zephyr software.
3) Reference documents for Zephyr. (Having these on the main page
instead of a sub-page make sense, since the API guide and
configuration option guide will be consulted frequently by users.)
Change-Id: Ifee7ac83f041c24e1efbe3ba7379c21a2ba8b9bc
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
fa2e040198