Get a hash with names and values of all instance variables.
class Foo < Struct.new(:name, :age, :gender); end
f = Foo.new("Jill", 50, :female)
f.attributes #=> {:name => "Jill", :age => 50, :gender => :female}
@return [Hash] Hash of
instance variables in receiver, keyed by ivar name
@api public