add chipmunk physics package

How do I know the test ran successfully?

```
$ make chipmunk
[target]   i686-pc-mingw32.static with 1 goal from command line
[build]    chipmunk
[done]     chipmunk
```
You can simplify this as:

```
$(PKG)_URL      := https://github.com/slembcke/Chipmunk2D/archive/Chipmunk-$($(PKG)_VERSION).tar.gz
```