Refactor code to make it possible to use with Boot

[nha]

I get this is a leiningen task.

I am sure there are people using boot that would be interested (I am one).

This project could either provide a boot task, or expose functions that a boot task could use to render the graph, prune dependencies etc.

[hlship]

It's possible a bit of it could be rewritten to use pomengranate (the underlying wrapper around the Aether/Maven code) more directly; that would make it more reasonable to have Boot make use of the code. To be honest, it's a bit of a hack getting the dependencies, especially the full dependency tree.

[hlship]

There's also a few other things related to logging that are a bit Leiningen specific but that could be refactored (we pass around an options map everywhere, logging could be abstracted to functions added to the options map).

[nha]

So maybe steps towards boot compatibility would be:

• exposing a function that takes dependencies in a format vizdeps likes and returns an image file (or takes a path/file as parameter). This would make it usable from clojure code as a library, and therefore by boot down the road.

• providing a helper function that would go from (:dependencies pod/env) to the format you want, and maybe even a boot task using it. This would make it "batteries incuded" for boot users.

For context, I know boot has some facilities around dependencies like

• (:dependencies pod/env) to get the dependencies
• a pedantic namespace https://github.com/boot-clj/boot/blob/master/boot/pod/src/boot/pedantic.clj that could be interesting
• boot.util/dep-as-map
• probably some more, not sure about the full dependency tree yet.

Note: I did not dig into the vizdep code yet so it may not all make sense - or make sense at all. In any case 👍 for doing it - I was wishing for something like that.

[hlship]

I don't use Boot any more (I tend to use Joker where in the past I used Boot). I'm open to a reasonable PR to break the code up to be more easily leveraged by Boot, but don't have the bandwidth to do the work itself.