Provide meaningful memory stats

[alco]

This topic needs some more research into the tooling available in Erlang/OTP. At the very least we should show the number of allocations and GC cycles performed during a test to give some indication of how two given tests compare memory-wise.

Related resources:

• http://www.erlang.org/doc/man/instrument.html
• https://blog.heroku.com/archives/2013/11/7/logplex-down-the-rabbit-hole
• https://github.com/ferd/recon/blob/master/src/recon_alloc.erl