v1.17.0

Added

• Pluggable flag-level help text rendering via cli.DefaultFlagStringFunc
• context.GlobalBoolT was added as an analogue to context.GlobalBool
• Support for hiding commands by setting Hidden: true -- this will hide the
  commands in help output

Changed

• Float64Flag, IntFlag, and DurationFlag default values are no longer
  quoted in help text output.
• All flag types now include (default: {value}) strings following usage when a
  default value can be (reasonably) detected.
• IntSliceFlag and StringSliceFlag usage strings are now more consistent
  with non-slice flag types
• Apps now exit with a code of 3 if an unknown subcommand is specified
  (previously they printed "No help topic for...", but still exited 0. This
  makes it easier to script around apps built using cli since they can trust
  that a 0 exit code indicated a successful execution.
• cleanups based on Go Report Card
  feedback