adds create_all_BIDS_events_tsv
adds create_all_BIDS_events_tsv

this function creates the BIDS events tsv files, which show when the
stimuli are presented for each run. it contains similar information to
the GLM matrices, except it also shows the info for each exemplar, not
just the classes, and it does so in terms of seconds, not TRs.

billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences,billbrod/spatial-frequency-preferences