Update information for current codebase features

Several things like default mount options, mkfs options,
structures, etc are out of date.

This is just a first pass but gets some of the simpler
things.

Also a few minor clarifications, notes, etc were added.

A few odd-character hyphens got fixed as well.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>