Added Pry#memory_size= to set the size of _in_ and _out_

lib/pry/pry_instance.rb

@@ -39,7 +39,7 @@ class Pry
     attributes = [
                    :input, :output, :commands, :print,
                    :exception_handler, :hooks, :custom_completions,
-                   :prompt
+                   :prompt, :memory_size
                  ]
 
     attributes.each do |attribute|
@@ -50,10 +50,6 @@ class Pry
       send "#{key}=", value
     end
 
-    size = options[:memory_size] || Pry.memory_size
-    @input_array  = Pry::HistoryArray.new(size)
-    @output_array = Pry::HistoryArray.new(size)
-
     true
   end
 
@@ -77,6 +73,17 @@ class Pry
     end
   end
 
+  # @return [Integer] The maximum amount of objects remembered by the _in_ and
+  #   _out_ arrays. Defaults to 100.
+  def memory_size
+    @output_array.max_size
+  end
+
+  def memory_size=(size)
+    @input_array  = Pry::HistoryArray.new(size)
+    @output_array = Pry::HistoryArray.new(size)
+  end
+
   # Get nesting data.
   # This method should not need to be accessed directly.
   # @return [Array] The unparsed nesting information.