Real Wavelet Transform
rwt = RWT(x,nvoice,wavelet)
signal, dyadic length n=2^J, real-valued
number of voices/octave
string 'Gauss', 'DerGauss','Sombrero', 'Morlet'
matrix n by nscale where nscale = nvoice .* noctave
see sections 4.3.1 and 4.3.3 of Mallat's book