Update submodule update screenshot (fixes #128)

Recursive submodules require extra commands
Add dragndrop generator for mac
Add bilinear scaling and RGB surface (#87, #129)

Scaling mode added to config, access via options
menu
Fix 3x bilinear scaling
Fix config_test build and test
Fix build and MacOSX blitting

MacOSX has a different pixel format
RGBA byte order
Include SDLMain.m in Mac build
Fix mac compile of editor
Fix bottom row floor drawing on odd resoution heights