Mammoth

* Fix: npm 7 changed the behaviour of prepublish, causing the browser build not
to be updated before publishing to npm. We now use prepare instead of
prepublish, which has the same behaviour that prepublish previously had.

* Convert symbols in supported fonts to corresponding Unicode characters.

* When extracting raw text, convert tab elements to tab characters.

* Handle internal hyperlinks created with complex fields.

* Emit warning instead of throwing exception when image file cannot be found for
a:blip elements.

* Ignore w:u elements when w:val is missing.

* Only use the alt text of image elements as a fallback. If an alt attribute is
returned from ImgElement.convert, that value will now be preferred to the alt
text of the image element.

* Ignore w:u elements when w:val is missing.

* Emit warning instead of throwing exception when image file cannot be found for
a:blip elements.

* Add TypeScript declarations.

* When extracting raw text, convert tab elements to tab characters.

* Handle internal hyperlinks created with complex fields.

* Update JSZip to 3.2.0. This addresses CVE-2021-23413 in JSZip.