Added support for alias-list to artist entities

Signed-off-by: Sam Doshi <sam@metal-fish.co.uk>
Added support for alias-list to label entities

Signed-off-by: Sam Doshi <sam@metal-fish.co.uk>
Added support for alias-list to work entities

Signed-off-by: Sam Doshi <sam@metal-fish.co.uk>
Merge pull request #83 from samdoshi/aliases

Add support for attributes for aliases (fixes: #82)
Handle socket timeout errors

These errors can occur transiently, so we now retry when socket.timeout is
raised.

Signed-off-by: Adrian Sampson <adrian@radbox.org>