v1.15.0

Added

• A CHANGELOG.md file!
• Support for placeholders in flag usage strings
• App.Metadata map for arbitrary data/state management
• Set and GlobalSet methods on *cli.Context for altering values after
  parsing.
• Support for nested lookup of dot-delimited keys in structures loaded from
  YAML.

Changed

• The App.Action and Command.Action now prefer a return signature of
  func(*cli.Context) error, as defined by cli.ActionFunc. If a non-nil
  error is returned, there may be two outcomes:
  • If the error fulfills cli.ExitCoder, then os.Exit will be called
    automatically
  • Else the error is bubbled up and returned from App.Run
• Specifying an Action with the legacy return signature of
  func(*cli.Context) will produce a deprecation message to stderr
• Specifying an Action that is not a func type will produce a non-zero exit
  from App.Run
• Specifying an Action func that has an invalid (input) signature will
  produce a non-zero exit from App.Run

Deprecated

• 
  cli.App.RunAndExitOnError, which should now be done by returning an error
  that fulfills cli.ExitCoder to cli.App.Run.
• the legacy signature for
  cli.App.Action of func(*cli.Context), which should now have a return
  signature of func(*cli.Context) error, as defined by cli.ActionFunc.

Fixed

• Added missing *cli.Context.GlobalFloat64 method