Updating project helpers for upcoming updates.
Reorganization of submodules to support additional data stores.

- Worker broken into two submodules, 'pg' (postgresql workers) and 's3'
  (s3 workers)
- New blobstore submodule added to help abstract away specifics of
  datastore interaction
Adding support for Windows Azure Blob Service as a datastore.
Merge pull request #47 from socrata/azure-support

Enabling easy addition of new data stores, adding Windows Azure Blob Service support
Add Brian Oldfield as a contributor.
Fix __all__ to use strings

Also alphabetize all the import and __all__ list lines, now that some
of the lists of exported functions are getting long enough to be
harder to scan.

Alex Gaynor <alex.gaynor@gmail.com> caught this systematic mistake of
mine in code review.
Fixes #50
All tablespaces are now backedup alongside base postgres data.
Moving away from TarFile.extractall in favor of per-member handling using TarFile.extract.
Merge pull request #51 from socrata/backup-all-tablespaces

Added optional flag to backup all tablespaces in addition to core postgr...
Defaulting BackupInfo.spec to dict for backwards compatibility. Fixes #53
Update README.rst

fixed grammar
Merge pull request #54 from sneak/patch-1

Update README.rst
Add Jeffrey Paul as a contributor
Remove superflous out-of-date comment

The decision since that time that unification of configuration
for each backend will not be attempted.
Disable bucket name validation in s3_worker

This can cause problems when one is using IAM policies that
restrict actions to a prefix in the bucket.

Also avoids one API call in the common case where the bucket is valid,
although later calls that touch the bucket for the first time must be
ready for an invalid bucket to raise exceptions.
Alphabetize imports
Rework credential configuration management

Credentials are now opaque objects except to the specific blob store
implementation that uses them.  This is to allow worker function
signatures to retain the same signature between backend storage
implementations even though different backends have different methods
of authentication that go beyond the account name/password approach.

While doing this, teach the S3 credential regime a 'security token'
parameter, which allows use of keys vended by AWS STS.
Add tests stressing AWS STS credentials and functionality
Remove dead parameter for .delete_all