Enable (param string[] something) to accept arbitrary number of parameters.

[igadmg]

For declaring some command like this
[Command("run", "Run commandlet.")] public async Task RunCommandlet([Option(0)] string commandlet, [Option(1)] params string[] parameters)
if last indexed parameter is params then it will accept all leftover parameters from command line

For example myprog run CommandletName param1 param2 - param1 param2 will be put to parameters array
In case of myprog run CommandletName - parameters will be empty.

[neuecc]

I think it's ok, I'll try to merge it, thanks.

[neuecc]

@yatagarasu25
sorry, this feature was released in 4.2.3 but I've reverted in 4.2.4 because this test was failed.
815cad8
If this feature is needed, please modify the code and also add unit tests along with it.