New `ZFile` iterator, outputting `Event`s

The "highlevel" protozfitsreader from digicampipe was moved here. We propose to use this interface to read SST1M zfits files now:

from protozfitsreader import ZFile
file = ZFile(path)
print("number of events:", file.numrows)
for event in file:
    # do something with event
    pass

event is an instance of `protozfitsreader.Event`.