Fix the minimal version of SPH

Ok, I have now fixed the minimalistic implementation of SPH. That's the one that should be used as a template for other people to implement their stuff. It's overly documented and now works on all the test-cases we have in the examples directory.

Don't know if you want to look at this or not @pdraper given that it does not affect our default setup at all.

Solves #148 (closed).

Branch can be removed.

Status changed to merged

mentioned in commit 32ff7194

Compiles and runs...

mentioned in issue #148 (closed)