Make Concatenate work with negative page number parsers

[canro91]

Now, Concatenates only works if given parsers are in the same page or have positive page numbers.

Instead of using a property for PageNumber, create a method to pass the current page and the relative page Parsinator is currently trying to parse. Maybe introduce a method in the base class?

[Test]
public void Parse_ConcatenateTwoPagedParsersANegativeAndPositivePageNumber_ParsersValueFromBothParsersInGivenPages()
{
    var p = new Dictionary<String, IList<IParse>>
    {
        {
            "Key",
            new List<IParse>
            {
                new Concatenate(key: "Value", separator: "|", new List<IParse>
                {
                    new ParseFromRegex(key: "Result", pageNumber: -1, pattern: new Regex(@"Result:\s*(\w+)")),
                    new ParseFromRegex(key: "Value", pageNumber: 2, pattern: new Regex(@"Value:\s*(\d+)"))
                })
            }
        }
    };

    var lines = FromPagesText(
@"Page1 This is a dummy page    Page-3",
@"Page2 Value: 123456           Page-2",
@"Page3 Result: Foo             Page-1");

    var parser = new Parser(p);
    var ds = parser.Parse(lines);

    Assert.AreEqual("Foo|123456", ds["Key"]["Value"]);
}