Eventio

Add command line tools

We now provide three command line tools, to look into `eventio` files.

* `eventio_print_object_information` prints a table of container types, versions and counts.
* `eventio_print_structure` prints all containers and subcontainer decriptions in a file
* `eventio_plot_histograms` uses matlplotlib to plot the histograms stored in an eventio file

Add Histogram support

To see all histograms in a file, run


$ python examples/plot_hists.py /path/to/simtel/file

SimTel support

* Most simtel types got implemented
* Should be able to read CTA prod2, prod3b and prod4 simulations, both simtel and corsika

* Fix dtype of cherenkov photo electron image (float32 -> int32)
* Allow access to simtel history from `SimTelFile`

Support for zstandard compression and some corsika fixes

* Longitudinal block parsed correctly
* zstandard compression using optional dependency `zstandard`

* Don't parse the whole file on initialization
* Generate top-level objects one after the other
* only seeks forward