add new_version that creates a new version with modifications

private members...  also increase coverage back to 100%, delete
outdated comments..

this involved restructing the objectstore to be more of a complete
repo, keeping things like create_by_ref for new objects...

required common properties..

FileObject now has hashes and other properties, use realpath
for the dir to get common path

exist.

the blob object which is the base object that most people think of,
and changes the File Object to be more of a simple cache to a blob
object.  Still open if the file object is a simple cache object, or
references a specific blob object.