Use files metadata

[piranna]

Allow to search files using metadata like author, album... this will require to parse this data and add it to the index. Doing this would also allow to search exactly for the audio content instead of the full file (audio content + metadata) increasing quality of results and the number of available sources. To do so, file transfers will require to be changed from chunks to explicit tell what bytes do you want. Also this can allow to improve the metadata based on results from others.