Add OrdinalAttribute to define explicit column order

[dyatchenko]

Changes:

1. OrdinalAttribute was added to specify column order used in IDataReader
2. Several unit tests were added to test the ordinal functionality

The ordinal attribute can be used as shown below:

        public class ObjectReaderWithDefinedColumnsOrderType
        {
            [Ordinal(1)]
            public byte C { get; set; }
            [Ordinal(0)]
            public int? D { get; set; }
        }

• IDataReader object returned in ObjectReader.Create() will have columns order according to the defined attributes.
• If the attribute is not defined in the source class then alphabetical order is used.
• If two fields have the same Ordinal value then then alphabetical order is used.
• If the attribute is defined only for some properties then the columns are sorted by the ordinal values and then in alphabetical order (properties with no attributes are considered as -1 ordinal).

[mgravell]

I think I'm OK with this in general, however I'm going to make a minor tweak to remove the bit where it then does an implicit sort by name - that is a breaking behavior change, where-as sorting by Ordinal is fine if it doesn't change the order when that feature isn't used.

Thanks; merging, then tweaking a little.