defaultenv-2: make abort key to stop autoboot configurable ...

currently supported only two options: any key and ctrl-c
"any key" is default option.
To configure it, use:
nv autoboot_abort_key=any
or
nv autoboot_abort_key=ctrl-c

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: defaultenv-2: Change highlight to make ...

It's a make snippet, so change highlighting accordingly.

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

Documentation: defaultenv chapter from user manual. ...

A number of grammar fixes, typoes, font changes from the defaultenv-2
chapter.

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>