wrapper function for loading ms coco dataset

    Parameters:
    ----------
    image_set : str
        train2014, val2014, valminusminival2014, minival2014
    dirname: str
        root dir for coco
    shuffle: boolean
        initial shuffle

def load_coco(image_set, dirname, shuffle=False):
    """
    wrapper function for loading ms coco dataset

    Parameters:
    ----------
    image_set : str
        train2014, val2014, valminusminival2014, minival2014
    dirname: str
        root dir for coco
    shuffle: boolean
        initial shuffle
    """
    anno_files = ['instances_' + y.strip() + '.json' for y in image_set.split(',')]
    assert anno_files, "No image set specified"
    imdbs = []
    for af in anno_files:
        af_path = os.path.join(dirname, 'annotations', af)
        imdbs.append(Coco(af_path, dirname, shuffle=shuffle))
    if len(imdbs) > 1:
        return ConcatDB(imdbs, shuffle)
    else:
        return imdbs[0]