dead link to RusuDissertation in the tutorial how_features_work.rst

[csukuangfj]

Your Environment

• PCL Version: the master branch

Context

The link

http://files.rbrusu.com/publications/RusuPhDThesis.pdf

in

https://github.com/PointCloudLibrary/pcl/blob/master/doc/tutorials/content/how_features_work.rst

is not available

Expected Behavior

The link should be accessible.

Current Behavior

It is unaccessible.

Code to Reproduce

Access the link above.

Possible Solution

Fix the link.

[taketwo]

Here is a link to the thesis in the TUM library: http://mediatum.ub.tum.de/doc/800632/941254.pdf. I think it is future-proof to use this one.