Do not automatically call meta.SetID().
Do not store the metadata if the file is not stored.
Do not require that MetadataStorage also implement DocStorage.
stor -> storage
Drop Timestamp from Metadata.
Have Copy() simply set the ID to "".
Drop the Metadata.Doc method.
Clarify a comment.
c.Check -> c.Assert.
Merge pull request #78 from ericsnowcurrently/filestorage-fixes

Apply some fixes to filestorage.