 Usage:
 [J,Msp,Nsp]=mtfftpt (data,tapers,nfft,t,f,findx) - all arguments required
 Input: 
       data        (struct array of times with dimension channels/trials; 
                   also takes in 1d array of spike times as a column vector) 
       tapers      (precalculated tapers from dpss) 
       nfft        (length of padded data) 
       t           (time points at which tapers are calculated)
       f           (frequencies of evaluation)
       findx       (index corresponding to frequen