Simple C++ influence map with unit tests. Largely a rewrite from the prototype I hacked together at http://bl.ocks.org/mnem/87e8998f389f1aa30227 but less pretty because no graphics.
Ignore the Xcode project, it was just a handy editor. The src should compile
on any C++11 or greater compiler. Or you can remove the = delete markers
in influence_map.h and shift the copy and assign constructors into
the private section and it should compile with earlier C++ compilers.