State compile options

[matthiasbeyer]

We should somewhere state the compile options and how they are beeing enabled or disabled.

For example, we should state that there is the possibility of adding debug output to the compile options, but that it results in a fucking lot debug output.

Also, we should make use of compile options for compiling parts of the code with -O3, if the user wants this. But for this one, we should analyze the code and where are the bottlenecks. We could do this part now, but I guess it would be better after adding the thread safeness.

[matthiasbeyer]

This should probably go into the contributing file.