update doc

sbull: fix

root cause commits in linux-stable:
commit b4f42e2831ff9b9fa19252265d7c8985d47eefb9
Author: Jens Axboe <[email protected]>
Date:   Thu Apr 10 09:46:28 2014 -0600

    block: remove struct request buffer member

    This was used in the olden days, back when onions were proper
    yellow. Basically it mapped to the current buffer to be
    transferred. With highmem being added more than a decade ago,
    most drivers map pages out of a bio, and rq->buffer isn't
    pointing at anything valid.

    Convert old style drivers to just use bio_data().

    For the discard payload use case, just reference the page
    in the bio.

update README.md

update doc. already support 4.1

update README.md

update README.md

update README.md

update README.md

simple: rename simple_open

root cause commits in linux-stable:
commit 20955e891d828b2027281fe3295dae6af8e0423b
Author: Stephen Boyd <[email protected]>
Date:   Thu Apr 5 14:25:09 2012 -0700

    libfs: add simple_open()

sbull: Fix compiling warning

commits in linux-stable:
commit 5a7bbad27a410350e64a2d7f5ec18fc73836c14f
Author: Christoph Hellwig <[email protected]>
Date:   Mon Sep 12 12:12:01 2011 +0200

    block: remove support for bio remapping from ->make_request