MarkDownload 4+

- Remove hidden content before exporting (thanks @nhaouari !). This allows you to use a different extension (e.g. Adblock) to hide elements that would otherwise clutter up your export
- Fixes for Obsidian integration in Safari (thanks @aancw !)
- Keep a few more HTML tags that have no markdown equivalent (`u`, `ins`, `del`, `small`, `big`) (thanks @mnaoumov !)
- Add support for KaTeX formulas parsing (thanks @mnaoumov !)
- Fixed saving for options when imported from file (and show a little 'saved' indicator)
- Added a toggle for downloading images in the context menu and popup
- Added a link to the options in the popup
- Added some basic error handling to the popup
- Changes to how html inside code blocks is handled (thanks @mnaumov !)
- Treat codehilite without specified language as plaintext (thanks @mnaoumov !)
- Ensure sequential line breaks in `pre` are preserved in code blocks (thanks @mnaumov !)
- Update user guide link in README to point to GitHub
- Added keyboard shortcuts to copy selection / current tab to obsidian (user-definable in browsers that support that) (thanks @legolasdimir and @likeablob !)
- Select multiple tabs (hold crtl/cmd) then copy all tab urls as a markdown link list via keyboard shortcut or context menu (thanks @romanPrignon !)
- Allow users to include custom text such like `{date:YYYY-MM-DD}/`` in their Obsidian Folder Name setting (thanks @likeablob !)
- Fixed a small typo in the user guide (thanks @devon-research !)
- Fix for missing headings on sites like Substack (thanks @eactisgrosso !)
- Add support for websites using MathJax 3 (thanks @LeLocTai !)