Adapt PBD solver 2.0.1

[yangfengzzz]

I found there are alot API changes in PBD 2.0.1. In SPH code, PBDWrapper is releated to such modification.

#167 only fix the link with old pbd code. how can I fix it to adapt this new pbd solver?

[janbender]

That is a good point. I just recognized that the PBD version SPlisHSPlasH uses is not up-to-date. I will put this on my todo list.

[janbender]

I just updated to the new PBD version.