Entropy (wavelet packet)

`E = wentropy(X,T)`

`E = wentropy(X,T,P)`

[1] Coifman, R. R., and M. V.
Wickerhauser. "Entropy-based Algorithms for best basis selection." *IEEE
Transactions on Information Theory*. Vol. 38, Number 2, March 1992, pp.
713–718.

[2] Donoho, D. L., and I. M.
Johnstone. "Ideal denoising in an orthonormal basis chosen from a library of bases."
*Comptes Rendus Acad. Sci. Paris, Ser. I*. Vol. 319, 1994, pp.
1317–1322.