fs: nfs: Implement Linux rootarg ...

Add the root= parameter for NFS filesystems. We currently hardcode
v3 and tcp which probably needs to become configurable at some point.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: Minor editing changes to filesystems content. ...

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: Add new sphinxs docs ...

This is a rewrite of the Documentation in reStructuredText format using
Sphinx as build system, see http://sphinx-doc.org/.

The documentation is built into static html pages with 'make docs'.
The pages can be found under Documentation/html after building.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>