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
Move '_scalar_property' to '_helpers'.

Also, add explicit coverage for it.
Map 'Bucket.location' to a simple, scalar property.
Re-map 'Bucket.versioning' as a boolean property, 'versioning_enabled'.
Map HTTP error responses for storage onto specific exception classes.

Fixes #164.
Merge pull request #353 from tseaver/refactor-bucket_scalar_properties

Refactor bucket scalar properties
Recursively walk subclass tree to build code->exception class mapping.
Merge pull request #355 from tseaver/164-add_http_specific_exceptions

Fix #164:  Map HTTP error responses for storage onto specific exception classes.
Open privkey file in binary mode.

Fixes #361.
Merge pull request #362 from tseaver/361-open_privkey_file_in_binary_mode

Open privkey file in binary mode.