add Template::Benchmark::Engines::Mason2

Hello.

I tried by adding the Engine of Mason2.

<pre>
% script/benchmark_template_engines --only_plugin TextXslate
--- Starting Benchmarks --------------------------------------------------------
ETA: 4 benchmarks to run = 40 seconds minimum.
--- Template Benchmark @Fri Nov 15 16:58:01 2013 -------------------------------
TeXs       - Text::Xslate (3.0.1)
--- uncached_string ------------------------------------------------------------
       Rate TeXs
TeXs 5.36/s   --
--- uncached_disk --------------------------------------------------------------
       Rate TeXs
TeXs 4.39/s   --
--- disk_cache -----------------------------------------------------------------
      Rate TeXs
TeXs 281/s   --
--- instance_reuse -------------------------------------------------------------
       Rate TeXs
TeXs 7451/s   --
% script/benchmark_template_engines --only_plugin HTMLMason
--- Starting Benchmarks --------------------------------------------------------
ETA: 5 benchmarks to run = 50 seconds minimum.
--- Template Benchmark @Fri Nov 15 17:00:46 2013 -------------------------------
HM         - HTML::Mason (1.52)
--- uncached_string ------------------------------------------------------------
     Rate HM
HM 22.5/s --
--- uncached_disk --------------------------------------------------------------
     Rate HM
HM 23.4/s --
--- disk_cache -----------------------------------------------------------------
    Rate HM
HM 104/s --
--- memory_cache ---------------------------------------------------------------
     Rate HM
HM 96.5/s --
--- instance_reuse -------------------------------------------------------------
     Rate HM
HM 1145/s --
% script/benchmark_template_engines --only_plugin Mason2
--- Starting Benchmarks --------------------------------------------------------
ETA: 3 benchmarks to run = 30 seconds minimum.
--- Template Benchmark @Fri Nov 15 17:06:26 2013 -------------------------------
M2         - Mason (2.20)
--- uncached_disk --------------------------------------------------------------
     Rate M2
M2 4.18/s --
--- disk_cache -----------------------------------------------------------------
     Rate M2
M2 43.2/s --
--- instance_reuse -------------------------------------------------------------
    Rate M2
M2 941/s --
</pre>