Axis Arrays and NRRD

[sjkelly]

The NRRD format is commonly used for dicom data exports. The NRRD FileIO loader produces an axis array, which is similar to the SDF format, but significantly more mature and feature-rich. In order to be useful for the julia medical/imaging communities, it might be good to have support for Axis Arrays to make the pipeline to a mesh far simpler.

[SimonDanisch]

cc @Kevin-Mattheus-Moerman

[sjkelly]

isosurface and AbstractMesh calls will now handle AbstractArray so HomogenousMesh(load("my.nrrd"), MarchingCubes()) will just work. See: https://juliageometry.github.io/Meshing.jl/dev/examples/#NRRD-Data-1