Source release 2.4.0 / SFML 2.4.0

CrSFML has been rewritten from scratch. It no longer uses CSFML (why?). The installation procedure has changed.

For a quick tour of the changes, see a diff from porting examples to the new version.

API changes

• Event is now an abstract struct, not a union (details)
• Structs no longer have to be created though separate constructor methods.
• Some classes and methods were renamed to be more consistent with SFML or Crystal rather than CSFML
  • Some classes become namespaced: FtpResponse → Ftp::Response
  • More getter methods (is_foo, has_foo) were changed to foo?
• Vector and Rect are proper generic types
  • The vector2 constructor method is now stricter, use vector2f or vector2i to avoid manual type conversions.
• The TransformableM module is gone, subclass or compose Transformable instead.
• Drawable module now must be included to pass the object to the draw method.
• Minor changes in function signatures - more consistent types, overloads and default arguments.
• Objects now keep references to the objects they store
  • No surprises or having to keep a reference to an object manually so it isn't deleted.
  • A getter will return the same object after setting it, not a different wrapper every time.