v1.2.0

Added

• Transform Unicode 13.0 emojis into SVG images (#167)
• Add MathJax v3 support to math plugin (#164, #165 by @tani, #166)
• Add sandbox directory to make easy to develop core (#157)

Changed

• Upgrade Marpit to v1.6.2 and Marpit SVG polyfill to v1.3.0 (#167)
• Upgrade dependent packages to the latest version (#167)