Add unreleased section to CHANGELOG post 0.16.1 release prep
Add unreleased section to CHANGELOG post 0.16.1 release prep

[skip ci]

CausalityLtd/ponyc,Perelandric/ponyc,dipinhora/ponyc,Praetonus/ponyc,jemc/ponyc,sgebbie/ponyc,boemmels/ponyc,ponylang/ponyc,dipinhora/ponyc,sgebbie/ponyc,Theodus/ponyc,Praetonus/ponyc,Perelandric/ponyc,CausalityLtd/ponyc,kulibali/ponyc,cquinn/ponyc,cquinn/ponyc,boemmels/ponyc,sgebbie/ponyc,Theodus/ponyc,Perelandric/ponyc,jemc/ponyc,Perelandric/ponyc,jemc/ponyc,boemmels/ponyc,ponylang/ponyc,sgebbie/ponyc,Theodus/ponyc,Theodus/ponyc,Theodus/ponyc,CausalityLtd/ponyc,dipinhora/ponyc,cquinn/ponyc,Praetonus/ponyc,sgebbie/ponyc,boemmels/ponyc,boemmels/ponyc,kulibali/ponyc,ponylang/ponyc,cquinn/ponyc,Perelandric/ponyc,Praetonus/ponyc,kulibali/ponyc,kulibali/ponyc