Idea: return the value in a KV pair more cleanly

[woodruffw]

Filing so I don't forget.

Right now, when we query foo.bar.baz, yamlpath will return the entire key-value pair for baz.

For example:

foo:
  bar:
    baz: abc

will yield baz: abc instead of just abc. This is intentional, since we often want the key as well for context when presenting spans.

On the other hand, sometimes we only want the value (e.g. as a starting offset/anchor for finding some substring of interest).

Consequently, it might be nice to have an API/API option that allows us to configure whether or not we get the key-value or just the value (or just the key).