Update Citation, increment version

[PhilippBach]

Thanks for contributing to DoubleML. Before submitting a PR, please take a look at our contribution guidelines. Additionally, please fill out the PR checklist below.

Description

• Increment version
• Update citation, include Journal of Statistical Software reference
• Rename format.perc ➡️ format_perc
• Fix http and broken URLs

Reference to Issues or PRs

Comments

PR Checklist

Please fill out this PR checklist (see our contributing guidelines for details).

• [x] The title of the pull request summarizes the changes made.
• [x] The PR contains a detailed description of all changes and additions.
• [x] References to related issues or PRs are added.
• [x] The code passes R CMD check and all (unit) tests (see our contributing guidelines for details).
• [ ] Enhancements or new feature are equipped with unit tests.
• [x] The changes adhere to the "mlr-style" standards (see our contributing guidelines for details).