CPU benchmarking and profiling

@hornairs @camilo @burke Please review

This adds time benchmarking and code profiling rake tasks to IDC.

We use mysql to generate 1000 rows with 5000 dependent associated records, and then benchmark/profile.

**Why?**
Lately there's been performance-related PRs.  This quantifies them.  You should see `rake benchmark:cpu` numbers go down for a performance improvement.  As well we can use this to look for regressions.  Liquid has this and it's super useful.