Measure complexity of C source

Complexity scans your C source code to help you:

* Locate suspicious areas in unfamiliar code
* Get an idea of how much effort may be required to understand that code
* Get an idea of the effort required to test a code base
* Provide a reminder to yourself. You may see what you've written as
  obvious, but others may not. It is useful to have a hint about what code may
  seem harder to understand by others, and then decide if some rework may be in
  order.