DOC: Add description of overflow errorrs
DOC: Add description of overflow errorrs

Unlike Python, NumPy integers have fixed sizes. This can lead to
confusion when a integer overflow occurs and users expect NumPy integer
types to behave similarily to Python integers. This commit explains
integer overflow, an example and potential work arounds.

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