Now the real last edition in module 'sigproc_test'.

Signed-off-by: Eduardo Tenorio <embatbr@gmail.com>
Fixing function 'filterbanks' (name changed to 'filterbank', in the singular) and writing it's test.

Signed-off-by: Eduardo Tenorio <embatbr@gmail.com>
Tests in module 'features_test' for function 'filterbank' from module 'features' completed.

Signed-off-by: Eduardo Tenorio <embatbr@gmail.com>