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.
Can the dir_data_entsize method just figure out itself which version to use?  To me, it's messy to have these dir2 / dir3 checks all over the place.  I feel like there should just be one `dir_` method that itself figures out the version.