New service: VHX.tv

Rough description of the steps involved:

1. Extract a magic ID from the URL
2. Generate a new URL from the ID and a hard coded string
3. Download this via HTTP
4. Decode the response as JSON. The result is an str->str dict.
5. Get the key 'hls' and download the URL this corresponds to
6. Send this to fetcher.hls.hlsparse and yield HLS streams

In step 5 one could also download the video via HTTP (key 'mp4') or RTMP (keys
'rtmp' and 'rtmp_540'). I chose to implement HLS download for no particular
reason.