External exemplars, more predictions images, more parametrized inference...

[GioFic95]

Added:

• requirements.txt file;
• possibility to use external exemplars in FSC_test_cross(few-shot).py via the --external parameter: all the test images share the same exemplars, given in the standard annotations json file, but only for few input images;
• visualisation of meaningful images even with small exemplars (s_cnt >= 1) in demo.py and FSC_test_cross(few-shot).py;
• writing of images with predictions and bounding boxes (the latter only if not "external") for each test image in FSC_test_cross(few-shot).py;
• writing of a plot with the number of counted objects for each input image in FSC_test_cross(zero-shot).py (particularly useful when doing inference on video frames);
• parameters to define all the needed input files and directories (anno_file, data_split_file, im_dir);
• parametrized limit to the number of exemplars used for any test image in FSC_test_cross(few-shot).py via the --box_bound parameter;
• possibility to disable test-time normalization in FSC_test_cross(few-shot).py via the --normalization parameter;
• print of elapsed time in demo.py.