Working draft Memory Arena extension

[devcarbon-com]

Hi Bodmer,

Here is a working-draft memory arena sprite feature that I ended up using for one of my clients projects. I'm sure there is a lot of design considerations and changes that should take place and what not, but figured I would give you the pull request so you can use it as a starting point if you are interested in adding it as a feature to the main repository.

My use-case was that most of the time, having a frame buffer was the priority. But for a certain feature, the extra ram was needed, and using a memory arena was chosen to prevent fragmentation.

Thank you very much for this library. It has been tremendously useful for me for my work.