Calculate KemptonTaylor Q index of alpha diversity.
Estimates the slope of the cumulative abundance curve in the interquantile range. By default, uses lower and upper quartiles, rounding inwards.
Parameters:  counts : 1D array_like, int
lower_quantile : float, optional
upper_quantile : float, optional


Returns:  double

Notes
The index is defined in [R48]. The implementation here is based on the description given in the SDRIV online manual [R49].
The implementation provided here differs slightly from the results given in Magurran 1998. Specifically, we have 14 in the numerator rather than 15. Magurran recommends counting half of the OTUs with the same # counts as the point where the UQ falls and the point where the LQ falls, but the justification for this is unclear (e.g. if there were a very large # OTUs that just overlapped one of the quantiles, the results would be considerably off). Leaving the calculation asis for now, but consider changing.
References
[R48]  (1, 2) Kempton, R. A. and Taylor, L. R. (1976) Models and statistics for species diversity. Nature, 262, 818820. 
[R49]  (1, 2) http://www.piscesconservation.com/sdrhelp/index.html 