[FEATURE] calibrate diameter with command line

[jazberna1]

Is your feature request related to a problem? Please describe.
This is a feature request I believe:
I would like to be able to run cellpose on the command line so that the diameter was estimated as in the GUI with the calibrate buttom. Otherwsie I have to load and image in the GUI, calibrate it, and then run all my images (from the same dataset) with the diameter from that single image I used for the calibration.

Describe the solution you'd like
To have a --calibrate boolean option that calibrates the image when enabled

Describe alternatives you've considered
According to the documentation I thought that setting the --diameter 0 would force the estimation of the diameter

--diameter
cell diameter, if 0 will use the diameter of the training labels used in the model, or with built-in model will estimate diameter for each image

However setting --diameter 0 actually produces an error when running cellpose. This is the full traceback

Traceback (most recent call last):
  File "C:\Users\malieva\miniconda3\envs\cellpose\lib\runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Users\malieva\miniconda3\envs\cellpose\lib\runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "C:\Users\malieva\miniconda3\envs\cellpose\lib\site-packages\cellpose\__main__.py", line 358, in <module>
    main()
  File "C:\Users\malieva\miniconda3\envs\cellpose\lib\site-packages\cellpose\__main__.py", line 205, in main
    out = model.eval(
  File "C:\Users\malieva\miniconda3\envs\cellpose\lib\site-packages\cellpose\models.py", line 187, in eval
    diams, _ = self.sz.eval(x, channels=channels, channel_axis=channel_axis,
  File "C:\Users\malieva\miniconda3\envs\cellpose\lib\site-packages\cellpose\models.py", line 773, in eval
    diam_style = self.diam_mean if (diam_style == 0 or
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Thanks
Jorge