Port of M. Kaess' AprilTags library from 2012 released.

This is a release – I released my version of Michael Kaess’ version of his AprilTags library, on Github. (Got that?)

Michael Kaess’ version was public on BitBucket, but it wasn’t building or up-to-date; not surprising given it was from 2012. So I updated it as follows:

• Updating to OpenCV 3.x
• Updating changes in Eigen
• Creating a cmake build process so the library can be included in projects with find_package(apriltags REQUIRED)

There’s a few reasons I did this; prior post about it is here.