Minor usability tweaks

[maxlandon]

• Use mvdan/sh for parsing and removing comments
• Update readline dep
• Update carapace dependency library
• Update readline dependency
• Ensure the completion function is initialized
• Update completer.go
• Update carapace to latest
• allow passing in your own context
• print errors to stderr insteas of stdout
• explicit return of err
• properly handle cancel error cause
• fix example command
• implement custom error types
• reuse AddHistorySource in AddHistorySourceFile
• proper reset flags between executions
• Update readline
• Fix Start