Fix TypeParse detection for decimal type

The TypeParse detection used in Utility.FlattenWorker threw a
System.Reflection.AmbiguousMatchException when being run on a decimal
property inside a custom class used in DataTable.New.FromEnumerable.
This was happening because there are two TryParse overloads for this
data type.

Modified the logic for this check to allow it to verify that any public
and static TryParse function exists for the given type.

Added unit test to verify that this is working for
DataTable.New.FromEnumerable with a class that has a decimal property,
related to #17.
Verify that RowAs works well with decimals
Merge pull request #28 from yellis/FromEnumerable

Fix TypeParse detection for decimal type