Stochastic Momentum Index
William Blau "Momentum, Direction, and Divergence",
John Wiley and Sons, Inc. 1995, ISBN 0-471-02729-4, page 29:
SM(q) = close - 0.5*(HH(q) + LL(q))
SMI(q, r, s) = 100*(EMA(EMA(SM(q), r)), s)/(0.5*EMA(EMA(HH(q)-LL(q)), r), s)
