Add REST api

[erodozer]

It could be nice to expose a REST api for your playlists/shares instead of a full rendered webpage. This could be valuable for exposing ftmp3 with chat bots, such as mumbledj or SystemD, to get links to your music or to play music over a voice chat.

[erodozer]

this can easily be added, the requirements will be either

1. Add a query string?format=json to the path
2. Add Accept-Type: application/json to the headers of the request

Should also provide an XML template if people want an xml instead of json response