Update release notes for 0.15.1
Update release notes for 0.15.1

gjhiggins/vcoincore,GroestlCoin/bitcoin,Jcing95/iop-hd,UFOCoins/ufo,BitzenyCoreDevelopers/bitzeny,Jcing95/iop-hd,particl/particl-core,wangxinxi/litecoin,romanornr/viacoin,digibyte/digibyte,digibyte/digibyte,wangxinxi/litecoin,qtumproject/qtum,tecnovert/particl-core,wangxinxi/litecoin,tecnovert/particl-core,Jcing95/iop-hd,particl/particl-core,UFOCoins/ufo,particl/particl-core,digibyte/digibyte,romanornr/viacoin,UFOCoins/ufo,tecnovert/particl-core,Jcing95/iop-hd,Anfauglith/iop-hd,gjhiggins/vcoincore,GroestlCoin/GroestlCoin,tecnovert/particl-core,GroestlCoin/GroestlCoin,Anfauglith/iop-hd,GroestlCoin/bitcoin,qtumproject/qtum,BitzenyCoreDevelopers/bitzeny,digibyte/digibyte,Anfauglith/iop-hd,particl/particl-core,gjhiggins/vcoincore,GroestlCoin/bitcoin,Jcing95/iop-hd,romanornr/viacoin,BitzenyCoreDevelopers/bitzeny,Anfauglith/iop-hd,Jcing95/iop-hd,gjhiggins/vcoincore,romanornr/viacoin,GroestlCoin/bitcoin,gjhiggins/vcoincore,BitzenyCoreDevelopers/bitzeny,romanornr/viacoin,romanornr/viacoin,UFOCoins/ufo,tecnovert/particl-core,digibyte/digibyte,GroestlCoin/GroestlCoin,wangxinxi/litecoin,qtumproject/qtum,GroestlCoin/bitcoin,particl/particl-core,BitzenyCoreDevelopers/bitzeny,qtumproject/qtum,wangxinxi/litecoin,UFOCoins/ufo,UFOCoins/ufo,qtumproject/qtum,wangxinxi/litecoin,gjhiggins/vcoincore,GroestlCoin/GroestlCoin,qtumproject/qtum,Anfauglith/iop-hd,GroestlCoin/GroestlCoin,digibyte/digibyte,tecnovert/particl-core,BitzenyCoreDevelopers/bitzeny,particl/particl-core,qtumproject/qtum,GroestlCoin/GroestlCoin,GroestlCoin/bitcoin,Anfauglith/iop-hd