2.8.0-rc1: Use Apache HttpClient directly

• IMPORTANT: Java 7 is now required. If you need Java 6 support, please
  continue using 2.7.0 or earlier.
• This library no longer uses Google HTTP Client. It now directly uses
  Apache HttpClient. Closes #40, #66.
• WebServiceClient now implements Closeable. A pool of connections will be
  kept alive to be used across requests. To ensure all connections are closed
  when the object goes out of scope, call close() or use the
  try-with-resource statement as appropriate.
• Setting of a proxy for the WebServiceClient is now supported by the
  proxy(Proxy) builder method.
• Updated documentation to reflect that the accuracy radius is now included
  in City.
• Updated dependencies.