Closed Feature: Create assertions for IDictionary [11048]

Assertions to support:
- ContainKey
- NotContainKey
- BeEmpty
- NotBeEmpty
- HaveCount
  Etc....

Example:
var dictionary = new Dictionary<int, string>() { { 1, "One" } };
dictionary.Should().ContainKey(1);
dictionary.Should().NotContainKey(2);
dictionary.Should().NotBeEmpty();
dictionary.Should().HaveCount(1);
Comments: Resolved with changeset 68313.