Support to show content based an expire field

As I mentioned in the title. Let's assume there is a data file below:
```yaml
hire: Want to hire a software enginner
expire: 2022-10-1
```

then, we can render the README file base on that. Show the content before `2020-10-01`.

Start by tracing how the YAML data file is parsed and how the README is rendered. Clarify whether the `expire` date includes or excludes the content, and which date comparison is intended. Done means README output consistently includes or omits the content according to the specified expiration rule, with coverage for the date boundary.

Written by the indexing model from the issue text.