STRF: batch_strf_delta and save_pstrf_delta added
typo fixed in pstrf_delta docs
STRF.batch_pstrf_delta now uses STRF.save_pstrf_delta
STRF.save_pstrf_delta now correctly saves lags
STRF.meanDeltaSTRF() modernized
* doc block added
* no longer requires stimulus name
* makes sure files exist in directory
* now auto-detects n_lags
* plot_kernels option removed
* old MDS plot code removed
STRF.meanDeltaSTRF demos added, readme updated