YAML comments support

[Tim203]

This adds support for YAML comments.
Let me know if you want to see changes.

[zml2008]

Thanks for this contribution! I would love to have full support for reading comments back from configuration files, but I think this could be a decent stopgap until that work is complete.

[Tim203]

I wasn't aware that comments are also supposed to be read back.
After quite a bit of digging I've added support for that in the latest commit.

I might change the way the comments are read back for map keys a bit, but the general concept is there.

Edit: made the changes

[kyngs]

Any update on this?

[zml2008]

no

[kyngs]

no

Sorry, should've asked differently: "What's stopping this from getting merged?"

[zml2008]

time

[zml2008]

I'm really not a fan of the fact that by creating a new root node here, we effectively construct two nodes per node when loading in a file

[Tim203]

You're then mainly talking about the mapping part right? When looking at the differences between a root node and a .node node it looks like only the path and parent differs.
We could add a method that works essentially like attachIfNecessary / parentEnsureAttached, but allows you to set the parent & path as well.

[szymon-off]

Is it currently possible to disable a new line being created before every comment? When defining comments using the @ Comment annotation, the generated file has an empty line before the comment itself.

For example:

@ConfigSerializable
public class MainConfig {
    @Comment("Fruit")
    String string = "Apple";
    @Comment("Number")
    int integer = 25 
}

will end up looking like this:

 
# Fruit
string: Apple

# Number
integer: 25

Other than that, this PR appears to be fully functional for my use case.