scripts: add changelog generator
scripts: add changelog generator

This adds a new script changelog.sh to generate changelog
entries automatically.

Fixes #2433

squeed/rkt,mike1729/rkt,alban/rkt,kinvolk/rkt,yifan-gu/rkt,sgotti/rkt,matthaias/rkt,achanda/rkt,coreos/rkt,akshaykarle/rkt,tmrts/rkt,jonboulle/rkt,sgotti/rkt,Wilybald/rkt,matthaias/rkt,rkt/rkt,alban/rkt,matthaias/rkt,akshaykarle/rkt,s-urbaniak/rkt,jjlakis/rkt,rkt/rkt,jonboulle/rkt,s-urbaniak/rkt,rkt/rkt,sstabellini/rkt,nhlfr/rkt,akshaykarle/rkt,tmrts/rkt,Wilybald/rkt,yifan-gu/rkt,tmrts/rkt,joshix/rkt,monstermunchkin/rkt,monstermunchkin/rkt,jjlakis/rkt,cab105/rkt,Wilybald/rkt,alban/rkt,nhlfr/rkt,markllama/rkt,ybubnov/rkt,Shashwatsh/rkt,cab105/rkt,jakon89/rkt,joshix/rkt,shobhit85/rkt,jakon89/rkt,jakon89/rkt,monstermunchkin/rkt,coreos/rkt,lucasallan/rkt,squeed/rkt,dgonyeo/rkt,sstabellini/rkt,Wilybald/rkt,yifan-gu/rkt,mike1729/rkt,ybubnov/rkt,s-urbaniak/rkt,shobhit85/rkt,joshix/rkt,yifan-gu/rocket,dgonyeo/rkt,kinvolk/rkt,joshix/rkt,kinvolk/rkt,yifan-gu/rocket,lucasallan/rkt,lucasallan/rkt,shobhit85/rkt,intelsdi-x/rkt,yifan-gu/rocket,dgonyeo/rkt,coreos/rkt,jonboulle/rkt,lucasallan/rkt,achanda/rkt,intelsdi-x/rkt,jjlakis/rkt,cab105/rkt,Shashwatsh/rkt,markllama/rkt,mike1729/rkt,achanda/rkt,euank/rkt,sstabellini/rkt,euank/rkt,markllama/rkt,nhlfr/rkt,kinvolk/rkt,intelsdi-x/rkt,Shashwatsh/rkt,euank/rkt,squeed/rkt,ybubnov/rkt,rkt/rkt,sgotti/rkt