echo nest: top-level code review pass
echo nest: top-level code review pass

General Python/beets style changes:
- "x is None" can generally be replaced with "not x"
- prefer iteration over repetitive lines
- config[foo].get(bool) can be replaced with config[foo] in conditions
- removed extraneous "return None", which is what Python functions do
  automatically if you don't return anything
- 79-column wrap

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