v0.4.0 (2021-04-25)

• Add support for system wide installation, --system flag (@PLPeeters, #149)
• Use ~ instead of $HOME for config dir (#136)
• Document stripping kernelspec (#141)
• Add support for removing empty cells (#131)
• Create directory for attributes file if needed (#139)
• Add support for stripping metadata keys containing periods (@baldwint, #143)
• Strip collapsible headings by default (@rpytel1, #142)