"Something like haxeshim"

We discuss this at every meetup but never opened an issue about it, so let's do that. The idea is to have something official that works similar to haxeshim. From what I gather, there are two main tasks for such a tool:

* deal with dependencies: figure out the dependencies, e.g. from `-lib` arguments, and prepare them for the actual compiler to consume
* allow self-updating the compiler: have a separate executable so that the actual compiler executable can easily self-update

I don't know much more about haxeshim, so I'll need some input here from various people: @back2dos @nadako @Gama11

I'm willing to work on this, but I'll need a clear understanding of what exactly we want to do.