Improve usage of ObjectSpace to include the classes of the objects

[kevinjalbert]

rake-mini-profiler has an profile-gc option which exposes finer memory allocation details. Most notability is that it shows the classes of the objects. This can be extracted using:

ObjectSpace.each_object.map{ |x| x.class.name }

This code will enumerate over all the objects in the ObjectSpace. From this we can more accurately store the number of objects from specific classes.

---

As a part of this improvement we should improve the way we store the individual object types in the ObjectSpaceStats. As we will be encountering dynamic object types we should instead of using fixed instance variables (i.e., string_count_collection), we should have an object_class_counts:

{
  "String" => [ 10, 12, 31],
  "NewRelic::Agent::NewRelicService::JsonMarshaller" => [1, 4, 3],
  "Integer" => [ 1, 1, 3],
  "RubyVM::InstructionSequence" => [3, 1, 1],
  ...
}

This should also simplify some of the verbosity of the source and specs.