Update changelog.
Update changelog.

xjzhou/PyMySQL,Ting-y/PyMySQL,Geoion/Tornado-MySQL,eibanez/PyMySQL,wraziens/PyMySQL,NunoEdgarGub1/PyMySQL,modulexcite/PyMySQL,wraziens/PyMySQL,mosquito/Tornado-MySQL,jwjohns/PyMySQL,pulsar314/Tornado-MySQL,nju520/PyMySQL,yeyinzhu3211/PyMySQL,PyMySQL/Tornado-MySQL,yeyinzhu3211/PyMySQL,lzedl/PyMySQL,pymysql/pymysql,MartinThoma/PyMySQL,PyMySQL/PyMySQL,jheld/PyMySQL,xjzhou/PyMySQL,methane/PyMySQL,DashaChuk/PyMySQL,boneyao/PyMySQL,anson-tang/PyMySQL,eibanez/PyMySQL,lzedl/PyMySQL