echonest: use pipeline stage
echonest: use pipeline stage

In addition to the performance benefit of running in our own thread, this also
obviates the need for the _songs dict to pass stuff between stages.

Freso/beets,m-urban/beets,shamangeorge/beets,arabenjamin/beets,kareemallen/beets,LordSputnik/beets,jcoady9/beets,shanemikel/beets,diego-plan9/beets,m-urban/beets,Kraymer/beets,Wen777/beets,dfc/beets,andremiller/beets,beetbox/beets,swt30/beets,lightwang1/beets,xsteadfastx/beets,marcuskrahl/beets,SusannaMaria/beets,lengtche/beets,untitaker/beets,bj-yinyan/beets,swt30/beets,Wen777/beets,jackwilsdon/beets,madmouser1/beets,m-urban/beets,untitaker/beets,swt30/beets,imsparsh/beets,pkess/beets,multikatt/beets,MyTunesFreeMusic/privacy-policy,marcuskrahl/beets,ibmibmibm/beets,sadatay/beets,PierreRust/beets,PierreRust/beets,lengtche/beets,jmwatte/beets,multikatt/beets,artemutin/beets,sampsyo/beets,ruippeixotog/beets,bj-yinyan/beets,sampsyo/beets,shamangeorge/beets,mosesfistos1/beetbox,drm00/beets,ruippeixotog/beets,diego-plan9/beets,ttsda/beets,MyTunesFreeMusic/privacy-policy,sadatay/beets,Freso/beets,beetbox/beets,Kraymer/beets,tima/beets,asteven/beets,dfc/beets,Wen777/beets,untitaker/beets,sadatay/beets,ttsda/beets,mried/beets,sampsyo/beets,PierreRust/beets,kelvinhammond/beets,imsparsh/beets,Dishwishy/beets,asteven/beets,mathstuf/beets,dfc/beets,parapente/beets,mosesfistos1/beetbox,mathstuf/beets,Andypsamp/CODfinalJUNIT,Freso/beets,kareemallen/beets,YetAnotherNerd/beets,andremiller/beets,diego-plan9/beets,arabenjamin/beets,gabrielaraujof/beets,LordSputnik/beets,mathstuf/beets,lengtche/beets,shanemikel/beets,tima/beets,kelvinhammond/beets,ibmibmibm/beets,jmwatte/beets,parapente/beets,YetAnotherNerd/beets,jackwilsdon/beets,mried/beets,Dishwishy/beets,MyTunesFreeMusic/privacy-policy,imsparsh/beets,arabenjamin/beets,lightwang1/beets,mosesfistos1/beetbox,MyTunesFreeMusic/privacy-policy,gabrielaraujof/beets,ruippeixotog/beets,pkess/beets,kelvinhammond/beets,LordSputnik/beets,moodboom/beets,beetbox/beets,ibmibmibm/beets,marcuskrahl/beets,kareemallen/beets,multikatt/beets,lightwang1/beets,krig/beets,Dishwishy/beets,arabenjamin/beets,pkess/beets,randybias/beets,randybias/beets,jackwilsdon/beets,xsteadfastx/beets,Freso/beets,Dishwishy/beets,ttsda/beets,dfc/beets,shanemikel/beets,swt30/beets,kelvinhammond/beets,mosesfistos1/beetbox,SusannaMaria/beets,Andypsamp/CODfinalJUNIT,artemutin/beets,LordSputnik/beets,jmwatte/beets,ibmibmibm/beets,jcoady9/beets,artemutin/beets,madmouser1/beets,shamangeorge/beets,marcuskrahl/beets,jcoady9/beets,andremiller/beets,bj-yinyan/beets,moodboom/beets,pkess/beets,Andypsamp/CODjunit,YetAnotherNerd/beets,moodboom/beets,Andypsamp/CODjunit,xsteadfastx/beets,drm00/beets,jackwilsdon/beets,Kraymer/beets,imsparsh/beets,parapente/beets,tima/beets,Kraymer/beets,madmouser1/beets,shanemikel/beets,krig/beets,ttsda/beets,Andypsamp/CODjunit,m-urban/beets,gabrielaraujof/beets,sampsyo/beets,untitaker/beets,randybias/beets,drm00/beets,mathstuf/beets,Andypsamp/CODjunit,Andypsamp/CODfinalJUNIT,YetAnotherNerd/beets,randybias/beets,shamangeorge/beets,jmwatte/beets,madmouser1/beets,asteven/beets,moodboom/beets,asteven/beets,Andypsamp/CODfinalJUNIT,beetbox/beets,drm00/beets,gabrielaraujof/beets,SusannaMaria/beets,Andypsamp/CODfinalJUNIT,bj-yinyan/beets,lightwang1/beets,sadatay/beets,jcoady9/beets,parapente/beets,artemutin/beets,mried/beets,Andypsamp/CODjunit,xsteadfastx/beets,mried/beets,krig/beets,lengtche/beets,diego-plan9/beets,PierreRust/beets,SusannaMaria/beets,tima/beets,ruippeixotog/beets,multikatt/beets,kareemallen/beets