STY Refactor alpha beta and rolling_beta calculation.
STY Refactor alpha beta and rolling_beta calculation.

YihaoLu/pyfolio,dursk/pyfolio,sketchytechky/pyfolio,yanheven/pyfolio,yanheven/pyfolio,raybuhr/pyfolio,chayapan/pyfolio,ChinaQuants/pyfolio,ChinaQuants/pyfolio,quantopian/pyfolio,quantopian/pyfolio,raybuhr/pyfolio,r0k3/pyfolio,sketchytechky/pyfolio,femtotrader/pyfolio,dursk/pyfolio,YihaoLu/pyfolio,femtotrader/pyfolio,r0k3/pyfolio