Update CHANGELOG with #607 and add version 3.0.0.dev1
Update CHANGELOG with #607 and add version 3.0.0.dev1

tareqalayan/pytest,The-Compiler/pytest,MichaelAquilina/pytest,pytest-dev/pytest,hpk42/pytest,vmalloc/dessert,hackebrot/pytest,pfctdayelise/pytest,flub/pytest,etataurov/pytest,Akasurde/pytest,txomon/pytest,jaraco/pytest,ddboline/pytest,hpk42/pytest,tomviner/pytest,nicoddemus/pytest,alfredodeza/pytest,The-Compiler/pytest,RonnyPfannschmidt/pytest,tomviner/pytest,skylarjhdownes/pytest,tgoodlet/pytest,malinoff/pytest,rmfitzpatrick/pytest,eli-b/pytest,davidszotten/pytest,nicoddemus/pytest,markshao/pytest