docs: move some of them to the root directory

docs: move some of them to the root directory

Lets move CodingStyle, SubmittingPatches, and Sponsors into the
root directory of netsniff-ng and remove the Documentation folder.
Some of those files are quite bloated, and most of these things
should be in the man-pages anyway. They should be the only big
sources of documentation, nothing else.

The rest is currently put here: http://pub.netsniff-ng.org/docs/

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>