Allow exporting HTML

[zrosenbauer]

Describe the problem you'd like to have solved

I need to be able to output HTML string.

Describe the ideal solution

A package for converting TempoJSON to TipTapJSON by adding options to the toJSON method.

const doc = new TempoDoc();

const output = doc
  .h1('Example')
  .paragraphy('Hello world!')
  .toString({ format: 'html' });

Alternatives and current work-arounds

Currently translate markdown to html using unifiedjs or other library.

Additional context

TipTap has an API but we need an OSS alternative.