Libmv 2D homography estimation example application

Add an example application of homography matrix estimation
from a 2D euclidean correspondences which is done in two
steps:

- Coarse algebraic estimation
- Fine refinement using Ceres minimizer

Nothing terribly exciting apart from an example of how to
use user callbacks.

User callback is used here to stop minimizer when average
of symmetric geometric distance becomes good enough.
This might be arguable whether it's the best way to go
(in some cases you would want to stop minimizer when
maximal symmetric distance is lower than a threshold) but
for a callback usage example it's good enough to stick
to current logic.

Change-Id: I60c8559cb10b001a0eb64ab71920c08bd68455b8
2 files changed