Add Click configuration

[maxvanliefde]

Some Click documentation is now unavailable. It was on http://read.cs.ucla.edu/click, can be found now on the wayback machine, for example https://web.archive.org/web/20170725130322/http://read.cs.ucla.edu/click

The Element Class Reference could be regenerated from comments in the code, see https://web.archive.org/web/20170630163322/http://read.cs.ucla.edu/click/doxygen/class_element.html for an example