bump version to v0.5.1
bump version to v0.5.1

faith0811/zerorpc-python,pchomik/zerorpc-python,joequant/zerorpc-python,jiajie999/zerorpc-python,nkhuyu/zerorpc-python,winggynOnly/zerorpc-python,Laeeth/zerorpc-python,ethifus/zerorpc-python,dotcloud/zerorpc-python,bombela/zerorpc-python,strawerry/zerorpc-python,virqin/zerorpc-python,stdrickforce/zerorpc-python,tempbottle/zerorpc-python,rainslytherin/zerorpc-python,lucius-feng/zerorpc-python