Fix #132:  enforce 64-bit ranges on long values for protobuf attrs.
Incorporate feedback from @dhermes.
Merge pull request #182 from tseaver/132-enforce_int64_bounds_for_protobuf_values

Fix #132:  enforce 64-bit ranges on long values for protobuf attrs.
Changing module docstring in storage __init__.

Also adding newline for PEP8 adherence.