Added

• Add shell completions, accessed by enabling the COMPLETE environment variable
  • For example, adding COMPLETE=fish slumber | source to your fish.config will enable completions for fish
  • See docs for more info and a list of supported shells
• Add slumber gen alias to --help documentation

Fixed

• Fix error loading requests with empty header values from history #400
• Fix input bindings involving shift and a character (e.g. shift g) #401