Bug Fixes

• $core: missing 404 page (close #2248) (#2250) (28a4eab)
• $core: duplicate meta tags (#2164) (01cd096)
• $plugin-search: match non-ASCII chars (close #2242) (#2283) (9f3f49c)
• $shared-utils: fail to resolve markdown-it plugins (close #2286)(#2289) (16df156)
• $theme-default: close dropdown on mouseout (fix #2227) (#2303) (430b917)