To do
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Feel free to implement these things:

Also there is no real limitation to electrical potential arrays, the
ExSimEck output strings should be adjusted to correctly handle 
magnetic pa. (Is there a sense in "E related output" for mags ?)

Option -S is reserved to future versions which will resolve potential
array's symmetry. In the present state symmetry only can be resolved
by SIMION itself.

Option -I is reserved to future versions which will resolve potential
arrays mirroring. This only is necessary in the extracting plane. One
have to derive the ion workbench coordinates from the symmetry, mirroring,
nx, ny, and nz, for being <coordinate> still a reasonable input parameter. 
(x=number: de-mirror y,z; y=number: de-mirror x,z; z=number: de-mirror x,y)
In the present state mirroring only can be resolved in working on the
output files.

There could be a 3d output instead of extracting a plane. Parameter
x=15 may lead to an extraction of the planes from x=15 to x=nx.
(How to manage the output file names?)

If there is no option file with given name it will be created.
