Based on a patch by Adrien Maglo.

Fix memleak. Return E_GENERIC instead of displaying an error message.
Signed-off-by: Laurent Aimar <fenrir@videolan.org>

Signed-off-by: Laurent Aimar <fenrir@videolan.org>

Signed-off-by: Laurent Aimar <fenrir@videolan.org>

 - XML encode everything (especially URL), not just some parameters,
 - use fputs() as appropriate,
 - remove a shadowed variable,
 - print duration as a 64-bits quantity.

I want to use function pointers in a later commit...

The Audio class can only be created/destroyed by the associated MediaPlayer
class. I will add some copy constructor later on.