Stage

Hello Guillaume,

First of all, thank you for your work.
I have question/proposition about Stage object. HLS class is very depended on Stage, but It's just a setter.
I recommend to move [Stage initialization](https://github.com/mangui/flashls/blob/81ecd8ce8b2ecd1f717d18b2a9168a3c7fa14837/src/org/mangui/hls/HLS.as#L174) in more important method. Anyway, with current implementation, library doesn't work without Stage. Or check for `Stage` could be earlier, before HTTP request to manifest.

Start with the Stage initialization linked in src/org/mangui/hls/HLS.as around line 174, then trace how HLS uses Stage before requesting the manifest. Compare the proposed initialization timing with an earlier Stage check, and verify that the library handles operation without Stage before any HTTP request.

Written by the indexing model from the issue text.