Introduced ValueCollectingVisitor
Made ValueCollectingVisitor implement IEnumerable<object>,

instead of the previous 'IEnumerable<T> with type filtering' behavior, which now seems like a slightly confusing API. Cleaned up tests based on review feedback.
Updated scenarios,

and deleted the old 'ValueCollectingVisitor' sample, since it's been promoted into a fully tested public API now. Also took the boy-scouting opportunity to use the 'ReflectionElementEnvy` methods in the scenarios.
Documented ValueCollectingVisitor.
Corrected variable name in test,

a good old cut&paste error.
Incremented minor version,

in order to indicate that the addition of a ValueCollectingVisitor is a
new feature. This resolves #50
(https://github.com/ploeh/Albedo/issues/50).