[x] Add file i/o support via user-specified filesystem that needs to include two (2) async methods: writeFile and readFile. See io folder for fileInput, fileOutput, stringInput and stringOutput.
[ ] Make sure usage in nodes with string and file IO works, along with usage in the browser also work. (Try making an vscode extension that works on the web with the vscode virtual filesystem!)
[ ] Finish porting the unit tests from docutils-typescript
[ ] Transformers (output is not currently processed as docutils would)
[ ] Directives (there are a couple of no-op directives in place, such as image and contents.)
[ ] Problems with sections
[ ] Problems with tables
[ ] Precise match of original python docutils output