When generating a view, there's now a way to reuse part of the directory
hierarchy of the parent branch. For example, `git annex view tag=* podcasts/=*`
makes a view where the first level is the tags, and the second level is
whatever `podcasts/*` directories the files were in.

Also, year and month metadata can be automatically recorded when
adding files to the annex. I made this only be done when annex.genmetadata
is turned on, to avoid polluting repositories that don't want to use metadata.

It would be nice if there was a way to add a hook script that's run
when files are added, to collect their metadata. I am not sure yet if
I am going to add that to git-annex though. It's already possible to do via
the regular git `post-commit` hook. Just make it look at the commit to see
what files were added, and then run `git annex metadata` to set their
metadata appropriately. It would be good to at least have an example of
such a script to eg, extract EXIF or ID3 metadata. Perhaps someone can
contribute one?