Add centimeters conversions to Margins, fix naming emus/twips

[PrzemyslawKlys]

• Allow conversion for margins from Centimeters to Emus and back;

public static void Example_BasicWordWithMarginsInCentimeters(string folderPath, bool openWord) {
    Console.WriteLine("[*] Creating standard document with margins");
    string filePath = System.IO.Path.Combine(folderPath, "EmptyDocumentWithMarginsCentimeters.docx");
    using (WordDocument document = WordDocument.Create(filePath)) {
        document.Sections[0].Margins.BottomCentimeters = 2.30;
        document.Sections[0].Margins.TopCentimeters = 5.50;
        document.Sections[0].Margins.LeftCentimeters = 3.01;
        document.Sections[0].Margins.RightCentimeters = 3.05;

        Console.WriteLine(document.Sections[0].Margins.BottomCentimeters);
        Console.WriteLine(document.Sections[0].Margins.TopCentimeters);
        Console.WriteLine(document.Sections[0].Margins.LeftCentimeters);
        Console.WriteLine(document.Sections[0].Margins.RightCentimeters);

        Console.WriteLine(document.Sections[0].Margins.Bottom);
        Console.WriteLine(document.Sections[0].Margins.Top);
        Console.WriteLine(document.Sections[0].Margins.Left.Value);
        Console.WriteLine(document.Sections[0].Margins.Right.Value);

        //document.Sections[0].Margins.Bottom = 10;
        //document.Sections[0].Margins.Top = 10;
        //document.Sections[0].Margins.Left = 600;
        //document.Sections[0].Margins.Right = 600;

        document.Settings.FontFamily = "Arial";
        document.Settings.FontSize = 9;

        document.AddParagraph("This should be Arial 9");

        var par = document.AddParagraph("This should be Tahoma 20");
        par.FontFamily = "Tahoma";
        par.FontSize = 20;

        document.Save(openWord);
    }
}

• Fix some names around twips/emus
• Added tests for conversions in TextBox/Margins
• Added some examples