[Ur] TechEmpower Benchmarks

[escalier at riseup.net]

I drafted a submission for the TechEmpower Web framework benchmarks
(results here: http://www.techempower.com/benchmarks/ | specs here:
http://www.techempower.com/benchmarks/#section=code&hw=i7&test=json).

Would anyone with more Ur/Web expertise be willing to look over my
submission?
(https://github.com/pseudonom/FrameworkBenchmarks/blob/master/UrWeb/bench.ur)

Areas that I know need attention:
- I defined my own `map2` rather than using `Top.map2` to avoid figuring
out the typing for `Top.map2`
- To get a list of random Ints of length x, I `List.mapM (fn _ => rand)`
over a range from 1 to x
- Ur/Web seems to expect an 'int8' where an 'int' would suffice
- Ur/Web seems to expect a 'text' where a 'varchar' would suffice

Thanks.