Add DateTimeOffset support to Sql Server

Sql Server supports DateTimeOffset, so treating it as a time loses a lot of data. This adds support for the column type. 

I've also added a note to ServiceStack.OrmLite/OrmLiteReadExtensions.cs. I'd like to find out if there's a better way to handle DialectProvider-specific formatting for parameters. The change I made was the only way to get querying with anonymous types to work.