Maint/puppet 4/document event manager

This adds documentation to `Puppet::Transaction::EventManager` and `Puppet::Resource::Status` and removes some dead attributes from `Status`.
There is a tendency to label "definition" as "declaration" in puppet - it throws me every time since a declaration is the introduction of a named (and possibly typed) entity but without definition of its value/content. We do not have that in puppet; a resource is always just defined (somewhere in a .pp source file typically).