Generate Singularity files

[nuest]

Generate singularity definition file for versions > 3.x, see https://www.sylabs.io/guides/3.0/user-guide/quick_start.html#singularity-definition-files and https://www.sylabs.io/guides/3.0/user-guide/definition_files.html

See also https://github.com/nuest/singularity-rstats (which could be based on containerit...) Paper: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0177459

• [ ] start with a function singularity_definition_file(..) using the same arguments as dockerfile. Worry about a wrapper function write_singularity_definition_file(containerit::containerit(from = ...))) later.
• [ ] take a look at https://github.com/mjstealey/rstudio
• [ ] add vignette
• [ ] re-read advice in #155 and check out https://github.com/singularityhub/singularity-compose-examples/tree/master/rstudio-simple

[nuest]

https://github.com/dynverse/babelwhale