The refactoring is required since completion is also supported for zsh
shell.
Refactoring details:
- flag generate-bash-completion -> generate-completion
- var EnableBashCompletion -> EnableShellCompletion
- var BashComplete -> ShellComplete
- var BashCompletionFlag -> GenerateCompletionFlag
- type BashCompleteFunc -> ShellCompleteFunc
by defining `cli.DefaultFlagStringFunc` with a default value that uses
`withEnvHint`, conditionally running a given flag's `FormatValueHelp` if
present.
Closes#257
Now the exit code can be returned by BeforeFn, ActionFn and AfterFn.
The `os.Exit` function is not called by this packaged
This closes#66 and closes#164