Add 3 online compilers found on isocpp

The following online compilers are added:
* [Rextester(Clang, GCC, MSVC)](http://rextester.com/runcode) - Online compiler which supports several compilers and different editors.
* [Rise4Fun(MSVC)](http://webcompiler.cloudapp.net/) - Online Visual C++ compiler.
* [Wandbox((Clang, GCC – includes Boost))](http://melpon.org/wandbox/) - An online compiler with boost available.