Added benchmark for tracking allocation overhead

bench/allocation_overhead_bench.rb

+require_relative 'benchmark_helper'
+
+Benchmark.ips do |bench|
+  bench.report 'disabled' do
+    'a' * 32
+  end
+
+  bench.report 'enabled' do |times|
+    Allocations.start
+
+    i = 0
+
+    while i < times
+      'a' * 32
+      i += 1
+    end
+
+    Allocations.stop
+  end
+
+  bench.compare!
+end