Benchmarks for stiff DDEs

[ChrisRackauckas]

@devmotion does the Enright DDE test problem set have some good stiff problems?

[devmotion]

At least there are no explicitly marked stiff problems.... But http://scholarpedia.org/article/Stiff_delay_equations contains some stiff DDE problems, and even mentions a neutral problem from Enright and Hayashi. However, to me it seems that the Enright test set only contains a similar neutral DDE but not exactly the same.

[devmotion]

Some test problems for RADAR5 are available on Hairer's site. Would be interesting to compare DelayDiffEq with RADAR5, but this would require both a Julia interface to RADAR5 (see luchr/ODEInterface.jl#6) and an JuliaDiffEq interface.

[ChrisRackauckas]

I wouldn't bank on it ever happening. But it would be nice to get the same tests as RADAR5 up and running to show we can do it.