Supporting TextBundle to publish to WordPress

Implementing open source library TextBundle makes it easy to publish notes to WordPress on iPad and iPhone.
https://github.com/shinyfrog/TextBundle

### What
Publishing Simplenote notes directly to Wordpress including styling (markdown).

### Why
Publishing notes, that are written in Simplenote, directly to Wordpress including styling would be very useful.

### How
TextBundle is an open source library for processing TextBundle files. WordPress already supports TextBundle. This would make it easy to publish notes to WordPress.
Bear built and implemented TextBundle and worked together with WordPress.
https://blog.bear.app/2019/05/introducing-a-new-way-to-publish-bear-notes-to-wordpress-on-ipad-and-iphone/

No repository files, tests, or entry points are named. Start by reviewing the linked TextBundle library and Bear's linked WordPress publishing example, then trace how Simplenote notes are exported on iPad and iPhone. Done means a note can be published to WordPress with its Markdown styling preserved.

Written by the indexing model from the issue text.