Urllib3 supports features left out of urllib and urllib2 libraries.

- Re-use the same socket connection for multiple requests (HTTPConnectionPool
and HTTPSConnectionPool) (with optional client-side certificate
verification).
- File posting (encode_multipart_formdata).
- Built-in redirection and retries (optional).
- Supports gzip and deflate decoding.
- Thread-safe and sanity-safe.
- Small and easy to understand codebase perfect for extending and
building upon.