A userscript that toggles all diff file viewed checkboxes

• Click the "Toggle viewed" button to set all "Viewed" checkboxes as either checked or unchecked. Checking all will collapse the files, making it easier to navigate the page.
• Alternatively, hold either the Shift or Alt key and toggle any of the "Viewed" file checkboxes to toggle all the files to match the selected file state.
• Click this link to install from GitHub; or, install from GreasyFork or OpenUserJS.

• Update dependencies

• Initial commit
• Add meta URLs

• Shared in https://github.com/Mottie/GitHub-userscripts/issues/120.