Add object profiling in addition to cpu profiling

In #380, I used object profiling to find some unnecessary object allocations on a hot path. In the comments, it was requested that this profiling be enabled by default so that others can use the data to potentially optimize further as well as a quick check for regressions.

Modified the profile code to run both cpu and object benchmarks, writing results to separate files for further exploration.

Review: @Shopify/liquid