Sync master changelog with v2.1 branch.
Sync master changelog with v2.1 branch.

Plexxi/st2,peak6/st2,Plexxi/st2,StackStorm/st2,Plexxi/st2,tonybaloney/st2,StackStorm/st2,nzlosh/st2,nzlosh/st2,peak6/st2,tonybaloney/st2,nzlosh/st2,tonybaloney/st2,StackStorm/st2,nzlosh/st2,peak6/st2,StackStorm/st2,Plexxi/st2