Support for Windows platform?

[maowtm]

Currently there is a few implicit assumption in the code that we're building Linux containers with Modus itself also running on Linux. These includes

• path.starts_with("/")
• Use of signal handlers

I don't know much about Windows containers - we might not even need to support them if they are quite rare and requires a lot of extra effort, but if we want Modus itself to be runnable on Windows then I will have to address the second point.

[thevirtuoso1973]

The buildkit_frontend library that we're using is also linux specific. However, this is because it uses an old version of mio.
We could fork and rewrite it with the new version of mio.

Otherwise right now it seems that we can't compile the project on (pure) Windows.

[maowtm]

I also noticed earlier that it uses tokio 0.x which can cause problem later if we add other dependencies, so I have been thinking of forking it. Haven't done so yet because it's not a problem for now, but I can do it if necessary