DOC: Add 1.13.0-changelog.rst
DOC: Add 1.13.0-changelog.rst

Create a new `doc/changelog/` directory and add the 1.13.0-changelog.rst
there.

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