Add schema dependency resolution

[ImFlog]

Intent to fix #12.

@oasalonen, I spent some time looking for something better than a plain list and thought that a Triple might be better.
Like this we know directly that what we send is the second of the triple and that the rest is here as dependencies. WDYT ?
Anyway this looks a lot like what you did in the first place.

[oasalonen]

Looks good. I would suggest one improvement to the ordering of the dependencies using the user->address->street example. If I understood correctly, right now the syntax would expect you to declare "user.avsc", ["street.avsc", "address.avsc"]. However, the dependency chain would be 'user depends on address depends on street' and as a user I would expect to write them in that order.

So how about you reverse the processing of the dependencies in the list, going from tail to head of the list so user's can write the chain as "user.avsc", ["address.avsc", "street.avsc"]?

[ImFlog]

This is a good idea, I'm doing the changes.

[ImFlog]

The version 0.4.0 is released and it embed this new feature.

[oasalonen]

I migrated back to your plugin release and the feature works. Thanks for integrating it!