doc: enforce 8-char tabs and 80-column width in coding standards

This will ensure uniformity in the future, but will require what code is
currently aligned on 4-char tabs to be reformated (basically the kernel
and arch code, and some other) to fit in 80 columns with 8-char tabs.
However, it will be more natural to developers used to 8-char tabs,
i.e. people used to work on Linux and other open source projects, which
is our audience, and will lower the barrier of entry.

Change-Id: I626b20e62ba1a5dddd030a27185f51237e5e98b5
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>