Allow to use yaml instead of json

Yaml is more convenient for writing and modifying big chunks of data. So my suggest is to add yaml support.

It is possible to do in 2 ways:
- add an option like `-data-yaml` (possibly with a short version `-Y`) for using instead of `-d`
- autodetect yaml if there is a `---` mark in the first line of data

The issue names no files, tests, or entry points; start by locating the CLI handling for the existing `-d` data input. Compare the two proposed YAML approaches, then verify that the selected interface accepts YAML data as described and add coverage for that behavior.

Written by the indexing model from the issue text.