Implement NodeWalker utility for traversing configuration structures

[lucko]

Provides a way to easily iterate over an entire configuration structure, or visit the child nodes in a specific sub section.

Use cases:

• most obvious I can think of is "printing" a configuration to a user
• searching for a specific value (less useful for configurations, but configurate can be used for reading and processing data too

I also intend to use this in SpongeCommon & GriefPrevention to exclude entries from being saved if they're already present & set to the same value in a "parent" config. Some sort of DFS post order traversal is needed to implement this behaviour, and I figured it made sense for that code to be in configurate itself, as opposed to being implemented in sub-projects.

Would appreciate any feedback :)

[liach]

can you make the node walker abstract class instead?

[lucko]

What would be the benefit?

[kashike]

I'd rather see a class like:

public abstract class NodeWalker {
    public static final NodeWalker BREADTH_FIRST = // ...
// ...

[lucko]

What would be the benefit?

[kashike]

Using an enum here restricts people from creating their own - can't extend an enum.

[lucko]

I don't foresee anyone doing this - but sure, point taken - will change.

Are you happy with the name NodeWalker? I'm not too sure on it

[kashike]

ConfigurationNodeWalker? ConfigurationNodeVisitor?

[lucko]

Hm yea, I think I prefer the first one

[lucko]

Okay, changed to ConfigurationNodeWalker and made the class abstract.