New package: MFCC (speech feature extraction)

Hi, 

Following your suggestions I contacted the people from DSP.  I re-wrote my Rasta package to use DSP instead of SignalProcessing (now obsolete), included Rasta in MFCCs and renamed this to MFCC, and changed the license for all code to BSD two-clause (permission from contributors Dan Ellis and Paul Kienzle), to make everybody happy. 

The DSP people do not want MFCC (speech feature extraction) into their package---they want to keep it pure signal processing, hence the proposal for a new Julia package.