includes support for converting 3D quad fields
found a minor error in field_on_axis, slightly wrong mid index was selected
some minor cleaning included

using loadtxt rather than genfromtxt
(did not need genfromtxt)
using skiprows and comments instead of header
do not assume z coordinate start at 0
Used to generate MEBT field maps

- Added auto-release to gitlab

thanks to Neven for discovering

updated the test file for density v11

I would normally expect for density file v11,
but I have earlier corrected it.
Now it was not working with our example file so I
corrected back.

fix trailing whitespace and end of line

- more consistent module names
- removing a duplicate
- fixing new flake8 warnings

replaced several string.format with f-strings

updated tracewin_errorstudy to python3
corrected errors from black/flake8