Property reflections include descriptions

Sometimes it's useful to access the description of a property (e.g. automatic admin form generation). Since YetORM's EntityProperty reflection already aggregates information about all the properties, it seems to be a good candidate for this.
Yup, we would have to forget about Strings::split()... Unless we ran it twice, first to check if there's a "->" and then with an appropriate limit (which would mean using preg_split directly).