graphics/poselib: Minimal solvers for calibrated camera pose estimation

PoseLib provides a collection of minimal solvers for camera pose
estimation.  The focus is on calibrated absolute pose estimation
problems from different types of correspondences (e.g. point-point,
point-line, line-point, line-line).

The goals of this project are to provide

 - Fast and robust implementation of the current state-of-the-art
   solvers.
 - Consistent calling interface between different solvers.
 - Minimize dependencies, both external (currently only Eigen) and
   internal.  Each solver is (mostly) stand-alone, making it easy
   to extract only a specific solver to integrate into other frameworks.
 - Robust estimators (based on LO-RANSAC) that just works out-of-the-box
   for most cases.

WWW: https://github.com/PoseLib/PoseLib