Refs. #5. Send digests in parallel.

When the pyzor script is configured to send to multiple server use
threading to send the digests in parallel to each server rather than
doing each request sequentially.
Refs. #5. Add tests for using pyzor with multiple servers.
Refs. #13. Add support for batched reports.

Add a new class BatchClient that will send batch send 10 digests to the specified servers. The batches are per server/per operation. Only report and whitelist operations are currently batched. Add support for multiple "Op-Digest" headers in the pyzor server.
Add more vebosity when test fail.
Refs. #13. Add tests for the batched report/whitelist functionality.
Refs. #13. Adjust the forwarder feature to use batched reporting.

The forwarder feature will now send reports and whitelists in batches
of 10 digests per address.
Separate the install and test running part in the travis config.
Typo.
Typos.
Various style improvements.

Have BatchClient batch_size be customizable. Use functools partial
and remove code duplication. Add posibility to flush out all
existing reports.

Avoid multiple threads writting on stdout simulteanously in the
pyzor script.
There is no inherit benefit in using __slots__.
Update documentation.

Add more information about getting the source code and running tests.
Also add more details about Pyzor dependecies and installation
procedure.
Catch invalid PV requests.
Adjust coverage call.
Update README.rst

Specify branch on coverage badge.
Refactor unit.test_client with the mock library.
Style fixes.
Add unittest for BatchClient.
Fix mock encoding test
Fix mock encoding test