minor fixes to feature computations

src/feat/feature-fbank-test.cc

src/feat/feature-fbank.cc

src/feat/feature-fbank.h

src/feat/feature-functions.cc

src/feat/feature-functions.h

src/feat/feature-mfcc-test.cc

src/feat/feature-mfcc.cc

src/feat/feature-mfcc.h

src/feat/feature-plp-test.cc

src/feat/feature-plp.cc

src/feat/feature-plp.h

src/feat/feature-spectrogram.cc

src/feat/feature-spectrogram.h

src/feat/mel-computations.cc

src/feat/mel-computations.h

src/feat/test_data/prepare_wav_in_ascii.m

src/feat/test_data/test_matlab.ascii

src/feat/wave-reader.cc

src/feat/wave-reader.h