Version 0.22-alpha

This version contains the following changes and new features:

• Debug target in Makefile
• Offset attribute for Sprite drawable
• Method for picking all nodes at a given point
• No audio or graphics driver support for applications with no sound or graphics
• Fix screenshot capture from game thread
• Drawable renamed to Component
• V-sync support on Raspbian
• Menu navigation with keyboard
• Bug fixes and improvements for OpenGL mesh buffer rendering
• Improved performance by filling the draw queue only when needed
• Removed global z order attribute from Node class
• Fullscreen support on Linux
• Lots of other bug fixes and performance improvements