* Updated the Android toolchain file to support NDKs up to the latest release (r12b; based on https://github.com/gongminmin/android-cmake).
* Fixed missing sRGB extension defines - also SFML once again compiles for older target API levels not having the sRGB extensions (fixes#1079, supersedes #1085).
* Changed SFML's default STL runtime to `stlport_shared`, since `c++_shared` is no longer supported.