Add '%m.%d.%y' date format for .mpr file timestamps

[chatcannon]

Closes #60

[chatcannon]

@regcs Could you test this and see if it works with your files?

[regcs]

@chatcannon Unfortunately, it still fails with a ValueError:

Traceback (most recent call last):
  File "2021-03-18 CV Auswertung - Figure 1.py", line 116, in <module>
    data_inkjet = read_mpr(file_inkjet, columns=headers, dtypes=dtypes)
  File "2021-03-18 CV Auswertung - Figure 1.py", line 47, in read_mpr
    file = BioLogic.MPRfile(mpr_file)
  File "/opt/anaconda3/lib/python3.8/site-packages/galvani/BioLogic.py", line 404, in __init__
    tm = time.strptime(settings_mod['date'].decode('ascii'), '%m-%d-%y')
  File "/opt/anaconda3/lib/python3.8/_strptime.py", line 562, in _strptime_time
    tt = _strptime(data_string, format)[0]
  File "/opt/anaconda3/lib/python3.8/_strptime.py", line 349, in _strptime
    raise ValueError("time data %r does not match format %r" %
ValueError: time data '11.12.20' does not match format '%m-%d-%y'

[chatcannon]

I see, there are two places with the different time formats but I have only changed one.

[chatcannon]

Try the new version and see if that works.

[chatcannon]

@regcs Any update? If you have no objections then I will merge this and push a new release to PyPI.

[regcs]

@chatcannon Sorry, I missed that. Looks good to me, thanks!