* Fix some library classes which failed, when Fox was not included into the global namespace.
* Add new accessor FXImage#dataPtr to access raw image data from FFI, Fiddle or OpenGL.
* Ensure zero terminated strings in values of C-argv.
* Remove various Ruby and C++ warnings.
* Update libfox to 1.6.57.
* Add support for RubyInstaller-2.6
* Set minimum required ruby version to 2.2