Lower required cmake version to 2.6
Add FindSFML cmake module
Use split up version of 2D-engine
Switch from setup.sh and build.sh to cmake.sh
Set cmake policy CMP0009 to NEW

NEW behavior: Do not follow symlinks when recursively globbing
OLD behavior: Do follow symlinks when recursively globbing

CMake 3.0.2 warns when this policy is not set and uses the OLD behavior.
Merge branch 'compatibility'