Implement benchmarks for deserialize, and deserialize & render

[peterzhu2118]

Based on #138.

Implements benchmarks for deserialize, and deserialize and render. Originally implemented in Shopify/liquid#1385.

Benchmark results:

              parse:    106.153  (± 0.9%) i/s -      1.070k in  10.081500s
             render:    216.622  (± 2.8%) i/s -      2.184k in  10.090715s
     parse & render:     62.163  (± 4.8%) i/s -    624.000  in  10.067989s
        deserialize:    152.583  (± 2.6%) i/s -      1.526k in  10.009992s
deserialize & render:
                         80.660  (± 2.5%) i/s -    808.000  in  10.023873s