Allow Volumes to be Resized

[beh9540]

Resize volumes per issue #177

[barakmich]

Close; it does change the spec on how big the volume is, but it doesn't actually change the volume size.

You'll want to use *File.Truncate() which appropriately grows or shrinks the file, and then writes the newly minted inode structure back.

I can adapt if you'd like, but you're most of the way there.

[beh9540]

@barakmich I'll fix it