Implement benchmarks for deserialization

[peterzhu2118]

Implement benchmarks for deserialize, and deserialize and render for Shopify/liquid-c#138.

Benchmark results:

              parse:    132.501  (± 3.0%) i/s -      1.326k in  10.019619s
             render:    236.153  (± 3.8%) i/s -      2.369k in  10.047556s
     parse & render:     75.737  (± 4.0%) i/s -    756.000  in  10.001978s
        deserialize:    163.091  (± 2.5%) i/s -      1.632k in  10.014565s
deserialize & render:
                         87.536  (± 2.3%) i/s -    880.000  in  10.060593s

[macournoyer]

Awesome! Very nice 👏

[dylanahsmith]

It seems like it would be a lot cleaner to do this in the liquid-c repo using a separate call to Benchmark.ips for "deserialize" and ":deserialize & render". We could load the theme_runner and extend it before running the benchmark.

[peterzhu2118]

Closing in favour of Shopify/liquid-c#141.