Add support for Akamai HD player verification to the HDS module

This requires passing in a hash identifying the player, combining it with a code from the manifest file, and then appending it to each fragment URL as a query string. So far I am using it to stream ABC Iview stuff (geo-restricted to Australia I understand) on the CLI, like this:

livestreamer hds://http://iviewum-vh.akamaihd.net/[. . .] pvhash='[. . .]'

The HDS URLs are printed by the _livestreamer_ branch of _python-iview_ at https://github.com/vadmium/python-iview.