Updated a check for denormalized values. Fixes occasional Inf values in EqualLoudness. Closes #160

Previosly this check was manually implemented and worked only for i386 and floats. Using std::fpclassify instead. This
solves the issue of Inf values in EqualLoudness algorithm output, and the consequent issue of Nan values in Spectrum
which was causing an infinite loop in SpectralPeaks.