add some latency benchmarks

[KristofferC]

Fixes #251

[ararslan]

1.0 failure: https://travis-ci.org/JuliaCI/BaseBenchmarks.jl/jobs/623222151#L1450

Internal error: encountered unexpected error in runtime:
StackOverflowError()
setindex! at ./essentials.jl:440 [inlined]
process_node! at ./compiler/ssair/ir.jl:760
process_node! at ./compiler/ssair/ir.jl:790 [inlined]
iterate at ./compiler/ssair/ir.jl:882
iterate at ./compiler/ssair/ir.jl:889
iterate at ./compiler/ssair/ir.jl:889
iterate at ./compiler/ssair/ir.jl:889
iterate at ./compiler/ssair/ir.jl:889
...

Seems not great.

[KristofferC]

Doesn't even seem to be from this PR though?

[KristofferC]

Passes now lul...

Oh, it passes even with the stackoverflow :package:

Should probably check that the plot is properly produced: https://travis-ci.org/JuliaCI/BaseBenchmarks.jl/jobs/623400233#L67244-L67251.