Event loop support

[melkyades]

Different platforms and frameworks use different apis for event loops:

• windows message pump
• gtk event loop
• SDL_WaitEvent loop
• http server callbacks
• etc

We need to create a series of objects that allow managing the complexity of different use cases while still being flexible enough.

• The event loop module(s) is(are) written in Smalltalk.
• There's no VM code to manage event loop
• All connections to the platform are done through ffi.