Add perf benchmarks based on fields

[mwchase]

See https://github.com/ionelmc/python-fields/blob/master/tests/test_perf.py

Maybe expand into separate benchmarks based on creation time vs access time.

My expectation is that adt.Product will be middle-of-the-road at best.
Need extra adaptors to pull of adt.Sum.

[mwchase]

Add coconut to the benchmarks as well.