Hint before resolving references in a tree

[captain-yoshi]

It would be awesome if we could query the ryml::Tree to see whether it encountered an anchor or an alias when parsing. By doing so, the user could have a hint to resolve or not the tree and thus skip the full traversal of the tree if there is no references.

Tree tree;
tree = ryml::parse_in_arena(buf)

// resolve if potential references
if(tree.has_ref())
    tree.resolve()

Maybe the API already does this but I did not find any way without traversing the tree.

[biojppm]

This is a good idea. I'll eventually get to this.