Add format flag to rwconfig for gyp project format support
Stubs for a particle system module
Improve module system

Each engine module now lives in its own isolated folder. Each module
consists of a "src" and "include/rosewood/<module-name>" subfolder.

Module dependencies - even those on a header-only level - now need
to be properly defined in the build system. This will ensure that module
separation and dependency order actually takes place.