PickleShare is a small shelve-like datastore with concurrency support.

Like shelve, a PickleShareDB object acts like a normal dictionary. Unlike
shelve, many processes can access the database simultaneously. Changing a value
in database is immediately visible to other processes accessing the same
database.

Concurrency is possible because the values are stored in separate files. Hence
the "database" is a directory where all files are governed by PickleShare.
