* Support some Unicode Mathematical Alphanumeric Symbols
This PR adds support for some of the characters in Unicode range U+1D400 to U+1D7FF, [Mathematical Alphanumeric Symbols](https://www.unicode.org/charts/PDF/U1D400.pdf). Specifically, it adds support for:
* A-Z a-z bold
* A-Z a-z bold italic
* A-Z a-z Fractur
* A-Z a-z sans-serif
* A-Z double struck
• A-Z script
Addresses issue #1215 and parts of #260.
* Fix lint error
* Fix MathML, and pick up review comments
* Fix lint error
* Add text mode. Remove sans-serif.
* Fix lint error
* Fixed \mathrm, added screenshotter test
* Change screenshotter test to an array
* Add screenshots
* Picked up review comments. Add characters
