Merge pull request #28 from mausch/master

Add generator for Nullable
Add bogus stacktrace message otherwise Xunit crashes
String and Object Arbitrary now generate and shrink null.
Update to VS2013
Released 0.9.3.
Update to F# 3.1.

Also remove unnecessary FSharp.Core reference from MSTest.Examples.
Fix generation of Dictionary.
Null value generation introduced in 17af4ae4b70750faf8c94c9a655ae6bce788449c broke it.
NonEmptyString should not generate null strings