Improve MethodHasPriority algorithm

[metoule]

This is mainly a fix for #191, but I also took the opportunity to improve the support of params arrays, to more closely match the C# specification.

For example, the following method calls are now properly resolved:

public static class Utils
{
  public static int WithParamsArray(params int[] i) => 3;
  public static int WithParamsArray(int i, params int[] j) => 4;
  public static int WithParamsArray(int i, int j) => 5;
}

var target = new Interpreter();
target.Reference(typeof(Utils));

var arr = new int[] { 2 };
target.SetVariable("arr", arr);

Assert.AreEqual(3, target.Eval("Utils.WithParamsArray(arr)"));
Assert.AreEqual(4, target.Eval("Utils.WithParamsArray(1)")); // improper call to int WithParamsArray(params int[] i)
Assert.AreEqual(4, target.Eval("Utils.WithParamsArray(1, arr)"));
Assert.AreEqual(5, target.Eval("Utils.WithParamsArray(1, 2)"));
Assert.AreEqual(4, target.Eval("Utils.WithParamsArray(1, 2, 3)")); // resolution failure 
Assert.AreEqual(4, target.Eval("Utils.WithParamsArray(1, 2, 3, 4)")); // resolution failure 

[davideicardi]

LGTM!