There are separate benchmarks for the Extras.cry module and the combined
Prelude + Extras module because the performance characteristics are nonlinear.
The benchmark suite no longer uses the `iteSolver` option.
Added a dependency on `deepseq-generics` so that the `NFData` instances
work correctly in Stackage LTS 2. Versions of `deepseq` before 1.4 have
a default instance that amounts to WHNF rather than NF, so benchmarks
were being measured incorrectly.
