useful for getting size distribution of known rois from each taxa. gathers size information from idsize text files produced when training a new classifier in VP (Visual Plankton)
vpr_trrois_size(directory, taxa, opticalSetting)
cruise directory eg. 'C:/data/IML2018051/'
list of character elements containing taxa of interest
VPR optical setting determining conversion between pixels and millimetres (options are 'S0', 'S1', 'S2', or 'S3')