maintenance

[vpbrendel]

The last accepted pull request led to a successful build of our Singularity container, but this was not the easiest of fixes. ngsutils has not been maintained for a few years (in its original package) and getting it to compile needed a peculiar fix (the code was compiled in a virtual python environment, but their latest commit had the necessary cython not be put into that environment, causing fatal compilation errors).

I suggest: 1) to freeze the current Singularity recipe/container with appropriate version labeling; and 2) consider building a new container with updated 3rd party software.