JSExportAttribute issues

[alexeybut]

@jasongin Thanks for quick #269 fix.
But I have found several issues:

Wrong comment for JSExportAttribute. You didn't add JSExcludeAttribute. Misprint publci.
/// When applied to an assembly, all public types in the assembly are exported, unless excluded
/// by another . When applied to a publci type, all public members
Some issues in IsExported(ISymbol symbol) method.
Please test the code:

[assembly: JSExport]
namespace Aspose.Words
{
    // Raises an exception.
    internal class Class1
    {
    }

    public class Class2
    {
        // Is exported.
        [JSExport(false)]
        public void ExportFalse()
        {
        }
        [JSExport(true)]
        public void ExportTrue()
        {
        }
    }
}

[alexeybut]

    [JSExport]
    public class Class2
    {
        // Exported
        public string Data { get; set; }
        [JSExport(false)]
        // Exported also
        public string Text { get; set; }
    }

[jasongin]

Thanks, apparently I did not test thoroughly enough. #275 fixes these issues.