Remove constraint on T for ParseArguments with factory

[pergardebrink]

Fix for #70 and #591

This makes it possible to have mutable types without empty constructor that only does explicit implementation of interfaces, like this (the IsMutable() check would fail previously in this particular case):

public interface IFoo {
    [Option("foobar")]
    string FooBar { get; set; }
}
public interface IBar {
    [Option("barfoo")]
    string BarFoo { get; set; }
}

public class FooBarOptions : IFoo, IBar {
    public FooBarOptions(string nonEmptyConstructor) { }
    IBar.BarFoo { get; set; }
    IFoo.FooBar { get; set; }
}

var result = Parser.Default.ParseArguments<FooBarOptions>(() => new FooBarOptions("foo"), args)

[moh-hassan]

Thanks @pergardebrink for your effort.
Nice that you fixed this missing issue.

[moh-hassan]

Just for correcting typo for the example in your post :

public class FooBarOptions : IFoo, IBar 
{
    public FooBarOptions(string nonEmptyConstructor) { }     
   string  IBar.BarFoo {get;set;}
   string  IFoo.FooBar { get; set; }   
}

[pergardebrink]

Thanks @pergardebrink for your effort.
Nice that you fixed this missing issue.

No problem, and thanks for accepting the PR!

I have another use case than my example that relied on having this working, so I was hoping to avoid forking the project just for that reason! ;)