Booklet

Changed the uuid package to uuid6, because it's on conda-forge.

added uuid version 7 as the uuid attribute.

The first 200 bytes of a booklet file can be passed at initialization to initialize a new booklet.

Added prune method, cleaned up some code, and added more details in the docs.

Upgraded with timestamps and metadata assignment. The VariableValue object can now be initialized with timestamp assignments. Whenever a key/value is stored, a timestamp is stored with it and the timestamp can be optionally specified (and changed later) by the user.
All of file metadata can also be assigned as a dict.
This is compatible with the previous 0.5 version.

Improved the checks and corrections when the file closes incorrectly. If it has, it will re-calculate the number of keys at reopening.