Find C++ header files that are slow to compile

This repo contains a simple tool to find which headers take the longest time to parse for any given input file. To see it in action, cd to the root of this repository and issue the following commands:

meson build
cd build
ninja
../slowfinder.py ../prog.cpp

The code has been tested with Meson but it should work with any build system that produces a compile_commands.json database.