Add Version 5 XFS Filesystem Support

Add support for Version 5 XFS filesystems.

This includes adding CRC fields to several on-disk
data structures including directory headers, as
well as allowing for a filetype field in the directory
entries.

A few Rubocop warnings in the code were fixed as well as
some style issues pointed out by @jrafanie and @Fryguy.

@Fryguy, @jrafanie, @roliveri, & @chessbyte please review
as appropriate.
Aren't all comments useless?  We all write self-documenting code, right?