add _pcl.pxd to share PointCloud def among Cython modules
wrapper for ICP: compiles, but untested
return transformation matrix from registration.icp, make max_iter optional
unit test for ICP
add generalized and non-linear ICP
registration tests: refactor, strengthen, assert instead of print
factor Eigen->NumPy conv. out of registration functions
pickle support for pcl.PointCloud