Add 'patman' patch generation, checking and submission script

Add 'patman' patch generation, checking and submission script

What is this?

=============

This tool is a Python script which:
- Creates patch directly from your branch
- Cleans them up by removing unwanted tags
- Inserts a cover letter with change lists
- Runs the patches through checkpatch.pl and its own checks
- Optionally emails them out to selected people

It is intended to automate patch creation and make it a less
error-prone process. It is useful for U-Boot and Linux work so far,
since it uses the checkpatch.pl script.

It is configured almost entirely by tags it finds in your commits.
This means that you can work on a number of different branches at
once, and keep the settings with each branch rather than having to
git format-patch, git send-email, etc. with the correct parameters
each time. So for example if you put:

in one of your commits, the series will be sent there.

See the README file for full details.
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Signed-off-by: Simon Glass <sjg@chromium.org>