manual: document that CSV is colon-separated.

Traditionally, CSV has meant comma-separated values, but in the context
of newfol, it always means colon-separated.  Document this.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
manual: document schema file format.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
manual: use Atx-style headers except for document title

These are easier to remember than using the Setext-style titles.  Also,
move the Data Layout section to a second-level title from a third-level.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>