switch from zip-stream to yazl
update to yazl 1
yazl 2. zipfile download shows accurate progress now.
yazl 2.0.1. fix 'write after end' error
Merge branch 'yazl'

Conflicts:
	package.json
multifile downloads use url parameters.

no need for body-parser dependency.
fixing zipfile name when multiple artists or albums are selected.
closes #339.
Merge branch 'master' into curlydiff
update curlydiff