Expose shared_ptr<OcTree>

[Jiayuan-Gu]

Add shared_ptr<OcTree>, otherwise there will be No to_python (by-value) converter found for C++ type error for python binding makeOcTree

[nim65s]

Thanks !

Could you add a simple regression test, reproducing this No to_python (by-value) converter found for C++ type error without your fix ?

[Jiayuan-Gu]

Em, I guess you need an example to reproduce. Here is a simple script to reproduce.

Install hpp-fcl=2.0.1

conda create -n test-hpp-fcl python=3.8
conda install hpp-fcl=2.0.1 -c conda-forge

And run

import hppfcl as fcl
import numpy as np
fcl.makeOctree(np.random.rand(5, 3), 0.001)

[jcarpent]

This PR looks good to me, as all other FCL primitives already use shared_ptr as Python container. Thanks @Jiayuan-Gu, your help is really appreciated.