Return hidden aliases as valid command (#10)

add support to hide aliases

Add HelpWriter field to customize help output (#8)

Add HelpWriter where the help output will be written. By default,
HelpWriter is set to os.Stdout.

HelpWriter can be set to writer that redirects the data to a terminal
pager for example.

allow flags with non-consecutive ordering (#7)

The current code assumes that all flags need to be consecutive, but it
doesn't have to be.  Refactor to ensure flags and args can be parsed
non-consecutively as well.

Adds 2 more constants to customize mc help content depending on the O…

…S. (#5)

* Adds 2 more constants to customize mc help content depending on the OS.
* Adds missing prompt to Unix style

Allow prompt, envSetCmd to work for sub-commands

Adds 3 more command help fields (#4)

Fix tests for new help templates.

Merge pull request urfave#569 from urfave/prepare-1-19-1

Prep 1.19.1

Update CHANGELOG