Add stackprof profiling tool

Entirely inconclusive, nearly all time is spent reading from hiredis for
'read-multi' operations.

Gemfile

@@ -10,4 +10,5 @@ group :benchmarking do
   gem 'oj'
   gem 'msgpack'
   gem 'redis-activesupport'
+  gem 'stackprof'
 end

benchmarks/profile.rb

@@ -0,0 +1,20 @@
+require 'bundler'
+
+Bundler.setup
+
+require 'fileutils'
+require 'stackprof'
+require 'readthis'
+
+readthis = Readthis::Cache.new('redis://localhost:6379/11')
+
+FileUtils.mkdir_p('tmp')
+readthis.clear
+
+('a'..'z').each { |key| readthis.write(key, key * 1024) }
+
+StackProf.run(mode: :object, interval: 500, out: "tmp/stackprof-object.dump") do
+  1000.times do
+    readthis.read_multi(*('a'..'z'))
+  end
+end