Bind touch API, adjustments to config

The project I'm working on currently involves using the touch API on linux, so I went ahead and bound it. Also, while testing on OS X, I was having trouble resolving some of the dllmaps, so I changed them to use the frameworks mechanism instead. The official SDL2 binaries for OS X are provided as frameworks, so this way probably reduces friction for users. A dllmap for OpenGL also seemed to be missing, so I added that.