TST: Removed perf_stats test, replaced with discrete tests for stats functions. Added tests for sortino, omega, and calmar.
TST: Removed perf_stats test, replaced with discrete tests for stats functions. Added tests for sortino, omega, and calmar.

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