Avoid re-iterating summary line.
Add accessors for read-only properties of a server-side object.

Addresses part of #313.
Add writable 'Key' properties matching writable server-side properties.

Addresses part of #314.
Factor out simple scalar property creation using helper methods.
Docstrings.
One-line docstrings.

Sigh.  That is *never* gonna look right to me.
Merge pull request #349 from tseaver/313-key_properties

Fix #313:  Add Key properties