Add exekall show subcommand
Allow showing the content of a ValueDB and exporting serialized objects:
# Show the value of an attribute of the object with the given UUID, or the object itself
$ exekall --debug show VALUE_DB.pickle.xz --show UUID_OF_A_RESULT.attribute
# Serialize an object or one of its attribute to the given PATH
$ exekall --debug show VALUE_DB.pickle.xz --serialize UUID_OF_A_RESULT.attribute PATH