Adds `NotBeNullOrEmpty` and `BeNullOrEmpty` assertions to Collection Assertions.
Merge pull request #74 from vossad01/Issue#63

Adds `NotBeNullOrEmpty` and `BeNullOrEmpty` assertions for collections
Merge pull request #73 from vossad01/Issue#6

Add DateTimeOffset Support
Correctes type parmeters of the AndConstraint<> objects returned by methods on StringCollectionAssertions