Switching from uproot3 to uproot4
Some simple changes were necessary to use uproot4 (new default uproot version) instead of uproot3. Basically some functions changed slightly their names (upper-lower cases: AsJagged and AsDtype) and it was necessary to explicitly set the library for filling the arrays (as: library="np", otherwise the default is "awkward" array). Furthermore the array name string has to be a simple string instead of a byte string (e.g.: b''). In the new branch [https://gitlab.mpcdf.mpg.de/ievo/ctapipe_io_magic/-/tree/dev-uproot4] these modifications are implemented. Since the strength of awkward arrays could be a speed-up of the run time we could investigate how to fully exploit this new resource before merging to master.