Store comments in the tree

[Strixpyrr]

For encoding, we should support adding comments to the file. Since an AddComment annotation is suggested in #114, I assume this is an intended feature. We'll need to add comments to the tree

Comments are likely to be "attached" to other elements, like:

# Comment
key = "value" # Other comment

So I think it makes sense to apply comments to a TomlNode instance, rather than being nodes themselves.

Something like this:

public sealed class TomlNode(
    public open val content: String,
    public open val lineNo: Int,
    public val comments: List<String>,
    public val inlineComment: String,
    public open val config: TomlConfig = TomlConfig()
)

Or:

data class TomlComments(
    public val comments: List<String>,
    public val inlineComments: String
)

public sealed class TomlNode(
    public open val content: String,
    public open val lineNo: Int,
    public val comments: TomlComments,
    public open val config: TomlConfig = TomlConfig()
)

We could also optionally retain or ignore comments during parsing with an ignoreComments property in the config