Adds Support For Indexes With Include Columns using SqlServerExtensions

When creating indexes for SQL Server that require include columns, you are forced to execute raw SQL.  This code is intended to allow indexes with include columns using the following syntax:

    Create.Index("IX").OnTable("TestTable").OnColumn("Id").Ascending().WithOptions().Include("Name");

This code shoould also support indexes with multiple include columns:

    Create.Index("IX").OnTable("TestTable").OnColumn("Id").Ascending().WithOptions().Include("Name").Include("DOB");

### Notes

It is worth noting, since this is an SQL Server specific feature it is only accessible as part of the [SQL Server Specific Extensions](https://github.com/schambers/fluentmigrator/wiki/Sql-Server-Specific-Extensions).

I have done my best to come up with a minimal set of unit tests to verify behaviour of this code.