Improve generic SMIL support
[YoutubeDL] format spec: correctly handle dashes and other unused operators
fixing xhamster file extraction
'mp4-baseline-16x9' must be handled as a single string, but the '-' was treated as an operator.
Eg. for VOD links like http://www.twitch.tv/gamesdonequick/v/9136645?t=14h29m15s