doc: Reorganized doc structure in root project folder

Moved the sphinx doc at project root folder, got rid
of source folder inside doc, updated Sphinx Makefile
and .gitignore to not track doc/build folder.

Change-Id: I1f169fa3b70269f24b10ee399bcac7cfa12e5695
Signed-off-by: Giuseppe Vallarelli <giuseppevallarelli@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/11627
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>