Complexes++ does not compile because of docs

[Clownshift]

Cmake errors, because it cannot find Doxyfile.in, where it is expected.
In CMakeLists.txt:
https://github.com/bio-phys/complexespp/blob/ba0396684b603e9bc1110672591782ce219d28d7/complexes%2B%2B/CMakeLists.txt#L166

However ../manual/ does not exist anymore after a781b32. It is now ../docs/
I will quickly fix that myself.