URL support

[Iago Toral Quiroga <itoral igalia com>]

Hi,

This is my proposal:

GRL_METADATA_KEY_URL

For the stream URL, that is, when we can provide the URI of the actual
stream. Example:

http://stream28.jamendo.com/stream/241/mp31/01%20-%20Both%20-%20Simple%
20Exercice.mp3?u=0&h=b92e063cc1

GRL_METADATA_KEY_WEB_URL: 

When the stream is playable on the web (like youtube), this is the URL
of web page for that resource. For example, in the case of Youtube:

http://www.youtube.com/watch?v=r5BFYGipokM

GRL_METADATA_KEY_PLAYER_URL

When there is a player available from that site, this is the URL of the
player object for that media item. For example, in the case of Youtube:

http://www.youtube.com/v/6m5KfDMlM78?f=videos&c=grilo&d=AT5TeR6GP1EiguaRg8tOw6MO88HsQjpE1a8d1GxQnGDm&app=youtube_gdata

Opinions?

Iago