Provide a way to identify static, run-time configuration & limits of SplinterDB library.

This issue was discussed as part of the review of PR #89 . We need ways to find out the limits that SplinterDB library has been compiled with, and also some indication of the configuration it's using.

Here are some thoughts / ideas to pursue:

• (ajhconway) Something related that I've wanted for awhile, but never put together is some sort of print_config() function that just dumps the current dynamic (and maybe also static) config.
• (rosenhouse) Related thought: I've been wondering if we can encode some of this metadata on disk. So that, say, a hypothetical CLI or debug tool could be pointed at a file or block device, discover the necessary config, and then open/work with the data.
• If we had some form of an error log where the library could dump out messages periodically, that log-file could be a place where the configuration in-use at startup, or at a change, could be recorded.
• It will also be useful to provide a simple interface to query the static / run-time configuration programatically. Application that is linked with library could then retrieve it.

Start by reviewing PR #89 and the issue's proposed directions: print_config(), on-disk metadata, error logging, and programmatic queries. Narrow these into one concrete interface that exposes SplinterDB's compiled limits and current runtime configuration; done should mean the selected configuration information can be retrieved or inspected unambiguously.