MAINT: advise implementing __array__ in duck arrays in NEP 30
MAINT: advise implementing __array__ in duck arrays in NEP 30

Edited NEP 30 to recommend that `__array__` be implemented *either* to return an ndarray or raise an Exception.

MSeifert04/numpy,mhvk/numpy,WarrenWeckesser/numpy,pdebuyl/numpy,WarrenWeckesser/numpy,grlee77/numpy,pdebuyl/numpy,grlee77/numpy,jakirkham/numpy,seberg/numpy,jorisvandenbossche/numpy,madphysicist/numpy,grlee77/numpy,mattip/numpy,abalkin/numpy,madphysicist/numpy,numpy/numpy,MSeifert04/numpy,WarrenWeckesser/numpy,seberg/numpy,simongibbons/numpy,charris/numpy,pbrod/numpy,MSeifert04/numpy,endolith/numpy,madphysicist/numpy,anntzer/numpy,WarrenWeckesser/numpy,pdebuyl/numpy,endolith/numpy,endolith/numpy,simongibbons/numpy,seberg/numpy,mhvk/numpy,pbrod/numpy,MSeifert04/numpy,rgommers/numpy,rgommers/numpy,endolith/numpy,MSeifert04/numpy,rgommers/numpy,madphysicist/numpy,simongibbons/numpy,WarrenWeckesser/numpy,pbrod/numpy,mattip/numpy,grlee77/numpy,rgommers/numpy,pbrod/numpy,pbrod/numpy,jorisvandenbossche/numpy,grlee77/numpy,jakirkham/numpy,numpy/numpy,numpy/numpy,jakirkham/numpy,anntzer/numpy,mhvk/numpy,jorisvandenbossche/numpy,abalkin/numpy,mattip/numpy,mattip/numpy,simongibbons/numpy,simongibbons/numpy,charris/numpy,pdebuyl/numpy,jakirkham/numpy,numpy/numpy,seberg/numpy,mhvk/numpy,jakirkham/numpy,mhvk/numpy,abalkin/numpy,charris/numpy,charris/numpy,anntzer/numpy,anntzer/numpy,madphysicist/numpy,jorisvandenbossche/numpy,jorisvandenbossche/numpy