SetName specific help text

Propose a smarter help text when SetName exists, prefer separated help text based on SetName, because the current help text doesn't tell users options in different SetNames are exclusive.

we could have help text as below:

**web** command:

--documentroot

--enablejavascript

-r

--help Display this help screen.

--version Display version information.

**ftp** command:

--ftpdirectory

--anonymouslogin

-r

--help Display this help screen.

--version Display version information.

Example option:

public class OptionsMutuallyExclusive
{
//Implement commands in set(group) named web
[Option(SetName = "web")]
public string DocumentRoot
{
get;
set;
}

[Option(SetName = "web")]
public bool EnableJavaScript
{
get;
set;
}

//Implement other commands in set(group) named ftp
[Option(SetName = "ftp")]
public string FtpDirectory
{
get;
set;
}

[Option(SetName = "ftp")]
public bool AnonymousLogin
{
get;
set;
}

//Common option, can be used with any set because it's not included in a set
[Option('r')]
public string UrlAddress
{
get;
set;
}
}