NH-3515 - Support for Decimal.Round, Decimal.Ceiling, Decimal.Floor and other static methods of Decimal class

**Alexander Zaytsev** created an [issue](https://nhibernate.jira.com/browse/NH-3515) — <time datetime="2013-08-21T20:45:50.763Z" title="2013-08-21T20:45:50.763Z">21st August 2013, 20:45:50</time>:
> Full list of methods available here: http://msdn.microsoft.com/ru-ru/library/System.Decimal_methods.aspx
> 