Expose TTL ZNode information

When a ZNode is created with a TTL, there is currently no way to later read the ZNode and determine:

1. Is the ZNode configured with a TTL?
2. When will the TTL expire?

This information could be useful, for example, where applications need to resurrect TTL-based tombstones into persistent ZNodes. Additionally, it would be useful for debugging via the CLI utility.

I would expect this information to be available via the Stat object.