Literature references requested in docs/source code

[NAThompson]

I had been studying the source code of this wonderful library since I was hoping to do a similar effort in C++. However, I have been unable to find the literature references for many of the algorithms.

Would it be possible to point to references in the docs? I know that (e.g.) adaptive differential evolution has so many flavors and variants that perhaps the key ideas can be consumed independently, making lit references rather painful. That said, I wasn't able to find "radius-limited differential evolution" anywhere . . .