Parse and generate YAML.

Please strongly prefer these high-level functions:
- [[parse-stream]]
- [[parse-string]]
- [[generate-stream]]
- [[generate-string]]
- [[marked?]] - relevant to `:mark` option when parsing only
- [[unmark]] - relevant to `:mark` option when parsing only

If history were to be rewritten we might have started with the above as
our public API.

The clj-commons/clj-yaml team noticed that folks were using other parts of
this namespace in the wild and therefore continue to support them.

If you find yourself using something in clj-yaml not listed above, it could be
you are doing so to overcome a limitation that we could address in clj-yaml itself.
If that's the case, we encourage you to work with us to potentially improve
clj-yaml for everybody. You can start by raising an issue and/or reaching out to us
on Slack.

General notes:
- We don't do any wrapping/conversion of SnakeYAML exceptions.
The SnakeYAML base exception is `org.yaml.snakeyaml.error.YAMLException`.
- Original YAML elements order is preserved with ordered set and map data structures,
currently via `org.flatland/ordered` lib.