* 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.
This is only implemented for Android builds and requires the user to include the sub-header specifically. Other platforms will trigger a compiler error, if they try to include this header file.
* Replaced the toolchain file with a new version based on [zuhowei's fork](https://github.com/zhuowei/android-cmake), which enables x64 builds as well as support for the latest NDK. This breaks compatibility with old build directories.
* Removed the STL dependency from **sfml-activity** rather than relying on *some* implementation implicitly linked by default.
* Deleted *project.properties*, which wasn't supposed to be part of the repository code. You have to use the Android SDK to recreate it (`android update project --path to/your/example --target 1 --name SFML-Example`).
* Made it possible to select a STL implementation to be used (default: `c++_shared`). Keep in mind that not all available configurations are necessarily compatible with SFML.
* Fixed linker flags to be compatible with Nvidia's Nsight Tegra for Visual Studio.
* It is now possible to compile the Android version using Nvidia's Nsight Tegra for Visual Studio (requires up-to-date CMake and `CMAKE_SFML_SYSTEM` to be set to `Android`; keep in mind that this is still experimental and requires further CMake updates).
* Updated and renamed some Android specific CMake variables.
* Made `armeabi-v7a` the default ABI for Android builds.
