The print dialog in the CHANGELOG and the widget catalogue
The commit that added `ltk::print` left both out. `CHANGELOG.md` gains its entry under Added, after `ltk::dirs`: what the dialog offers, how the app answers its requests for a preview, CUPS loaded at first use, the printers, jobs and default printer for a settings page, the print portal for an app in a Flatpak with `ltk::print::gtk` for a portal backend, zbus in the `wayland` feature, and only saving as PDF on Windows, Android and in a browser.
`docs/widgets.md` describes `print_dialog` among the pickers, after `file_chooser`, and links it from the table of contents: a component the app holds as it holds the file chooser, the preview the app renders on request, the job it delivers with `ltk::print::send`, and the builders that choose where it starts. Its example opens the dialog, answers its events and sends the PDF to a printer, and is compiled by `make doctest-md`.
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