Collision free chunk hashing

After much discussions and benchmarks in PullRequest #41 this is the final outcome with a better hashing function. It is now collision free for the typical chunk coordinates and therefore also slightly increases the overall performance. All the details can be found in the discussion of the old PullRequest #41.

I just rebased this branch to the latest changes in master, to get it ready to be merged now.
I'm sorry to have included some additional files in one of the old commits (only changing file mode), please ignore them during merge.