DOC: Warn about the difference between np.remainder and math.remainder
DOC: Warn about the difference between np.remainder and math.remainder

Python 3.7 adds its own `math.remainder` with different semantics to ours.
We can't change the semantics now, but we can warn users that they are different.

WarrenWeckesser/numpy,rgommers/numpy,jakirkham/numpy,simongibbons/numpy,jorisvandenbossche/numpy,simongibbons/numpy,mattip/numpy,pbrod/numpy,jakirkham/numpy,madphysicist/numpy,shoyer/numpy,jakirkham/numpy,mhvk/numpy,WarrenWeckesser/numpy,madphysicist/numpy,Eric89GXL/numpy,pizzathief/numpy,jakirkham/numpy,gfyoung/numpy,mhvk/numpy,mattip/numpy,charris/numpy,pdebuyl/numpy,pdebuyl/numpy,shoyer/numpy,shoyer/numpy,numpy/numpy,numpy/numpy,seberg/numpy,abalkin/numpy,mhvk/numpy,simongibbons/numpy,madphysicist/numpy,simongibbons/numpy,madphysicist/numpy,WarrenWeckesser/numpy,jorisvandenbossche/numpy,abalkin/numpy,pizzathief/numpy,shoyer/numpy,mattip/numpy,mhvk/numpy,pdebuyl/numpy,ahaldane/numpy,jakirkham/numpy,numpy/numpy,charris/numpy,Eric89GXL/numpy,endolith/numpy,tynn/numpy,gfyoung/numpy,ahaldane/numpy,ahaldane/numpy,grlee77/numpy,rgommers/numpy,MSeifert04/numpy,endolith/numpy,rgommers/numpy,abalkin/numpy,mattip/numpy,grlee77/numpy,Eric89GXL/numpy,mhvk/numpy,seberg/numpy,ahaldane/numpy,WarrenWeckesser/numpy,rgommers/numpy,grlee77/numpy,grlee77/numpy,pizzathief/numpy,tynn/numpy,anntzer/numpy,Eric89GXL/numpy,pbrod/numpy,pbrod/numpy,pizzathief/numpy,seberg/numpy,pbrod/numpy,charris/numpy,simongibbons/numpy,anntzer/numpy,anntzer/numpy,jorisvandenbossche/numpy,seberg/numpy,jorisvandenbossche/numpy,MSeifert04/numpy,MSeifert04/numpy,grlee77/numpy,pdebuyl/numpy,numpy/numpy,pbrod/numpy,gfyoung/numpy,endolith/numpy,MSeifert04/numpy,pizzathief/numpy,jorisvandenbossche/numpy,shoyer/numpy,madphysicist/numpy,WarrenWeckesser/numpy,MSeifert04/numpy,tynn/numpy,endolith/numpy,ahaldane/numpy,anntzer/numpy,charris/numpy