Introduced CompositeReflectionElement class.
Made CompositeReflectionElement class an Iterator.
Implemented IReflectionElement composite.
Added XML documentation to CompositeReflectionElement class.
Addressed a Code Analysis warning.
Introduced NullReflectionElement class.
Implemented NullReflectionElement.

This is (hopefully obviously) an implementation of the Null Object
pattern.
Documented NullReflectionElement.
Overrode Equals and GetHashCode.
Documented overriden methods.

This resolves #23 (https://github.com/ploeh/Albedo/issues/23).
Gave AssemblyElement Structural Equality.
Documented the Equals overload.
Documented overridden GetHashCode.
Gave TypeElement Structural Equality.
Added XML documentation.
Introduced IReflectionElementMaterializer

and AssemblyElementMaterializer, although the implementation is still
incorrect.
Added first implementation of Materialize,

although it's still degenerate.
Passed AssemblyElements through.
Passed any IReflectionElement through.
Preserved ordering during Materialization.