Added `Be` overload to NullableSimpleTimeSpanAssertions.  Allows `Be` assertions against Nullable<TimeSpan> which should fix issue #5.
Added Arrange, Act, Assert Comments in NullableSimpleTimeSpanAssertionSpecs.cs
Changed method names for new unit test to new format.
Merge pull request #38 from vossad01/Issue#5

Added `Be` overload to NullableSimpleTimeSpanAssertions.