3 years, 7 months ago.
It looks like that article describes the general concept and math of PID but it doesn't link to an exact library.
If you search for PID on the mbed site there are bunch of libraries that people have written.
This was one of the first libraries that popped up: https://developer.mbed.org/users/aberk/code/PID/
I haven't tried this library, but it looks like it has some examples to get you started (see the section maked Dependents near the top of the page).
Hope that helps!