Support for the 'Referer' header.
Add @BoD to contributors
Shadow header names in setter parameter names
Sort header name constants alphabetically
Add unit test for setting Referer header
[maven-release-plugin] prepare release http-request-5.3
[maven-release-plugin] prepare for next development iteration
Bump version to 5.3
Add ConnectionFactory abstraction for creating new HTTP connections.

This allows us to plug other `HttpUrlConnection`-compatible implementations
into the helpers.