Remove 'buffer_xwritev'

It does not have anything to do with a 'struct buffer'.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
Remove 'buffer_sendmsg'

It is just a wrapper for 'sendmsg'.

Signed-off-by: Jussi Virtanen <jussi.k.virtanen@gmail.com>
Merge pull request #27 from jvirtanen/cleanups/buffer-methods

Clean up 'struct buffer' methods