docs: use #!/usr/bin/env python shebang instead of #!/usr/bin/python ...

Some distributions might not have python in /usr/bin, but in $PATH.

Using #!/usr/bin/env python solves this, and is consistent with how the
other perl and python shebangs look like in the tree.

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

Documentation: make gen_commands helper python3 compatible ...

On some machines the python command is provided by Python 3 while on
most (at least in my bubble) it is still Python 2. Modify the code to
make it usable by both Python versions.

print_function is available in __future__ since Python 2.6.0a2, which
shouldn't be a relevant restriction.

The modified script generates the same documentation as the old one;
independent if the script is called using Python 2 (here: 2.7.16) or
Python 3 (here: 3.7.3).

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Documentation: handle missing group declaration ...

Use group 'misc' as a default and print a warning.

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>

Documentation: change generated help lines ...

Someone

   loadx (load binary file over serial line (X-Modem))

looked more silly than

   loadx - load binary file over serial line (X-Modem)

Signed-off-by: Holger Schurig <holgerschurig@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation: only write changed *.rst files ...

Documentation/gen_commands.py use to re-write all auto-generated *.rst
file, changed or not. That in turn didn't work well with the internal
cache of the Sphinx documentation generator.

By comparing the SHA1 hash of the newly generated *.rst with the
current sha1 file, the time to execute "make docs" can be reduced
from 6.2s to 2.4s on my humble laptop.

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

Documentation: use command groups ...

The help definition already contained a group declaration.
This is now reused for the HTML documentation.

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
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>