Update to more recent openCV version

[trsh]

2.4 is damn old

[rinogo]

I agree!

...but keep in mind that this is in the Readme:

I (@peterbraden) don't spend much time maintaining this library, it runs primarily on contributor support. I'm happy to accept most PR's if the tests run green, all new functionality is tested, and there are no objections in the PR.

So, who wants to volunteer to make the upgrades? 😁