stream.http: Some small changes.

- Use requets directly rather than urlget
- Let requests prepare the url property
stream.http: Make sure header keys are strings and not bytes.
Add a new exception that all other exceptions inherit from.
plugins.weeb: Remove usage of StreamError.
win32: Add some more comments to livestreamerrc.
cli: Refactor player output and add some new features.

- Add --player-args, allows more control over player command.
- Add --player-http, outputs stream over HTTP
- Add --player-continuous-http, outputs stream over HTTP (forever)
- Add --player-passthrough, passes compatible streams directly
  to the player as a filename.