Highlight/Format Markdown to Improve Readability

## What
Formatting the markdown text would make for a more pleasant and more productive experience without having to flip back and forth between Preview mode.

Simplenote already kind of does this for both ordered and unordered lists, so this is largely a continuation of that feature, which is obviously very helpful!

## Why
I was inspired to dream bigger for Simplenote after reading [this blog post](https://tonsky.me/blog/sublime-writer/). I've realized recently that I really want just a bit of basic markdown formatting ([example package for Sublime Text](https://github.com/SublimeText-Markdown/MarkdownEditing)) when writing. It would make my notes _significantly_ more readable.

The Preview function is useful in theory, but I find I almost never use it because I can't edit anything when in Preview mode and flipping back and forth is a hassle.

## How
Simplenote:

Markdown highlighting in Sublime Text:

"Hanging Punctuation" for Headings (image credit tonsky.com)

## Initial Ideas

### MVP Features
- Basic inline formatting for: bold, italic, links, code, (and strikethrough?)
- Block formatting for headings, blockquotes, code

### Features that would add polish
- ["Hanging" punctuation](https://tonsky.me/blog/sublime-writer/#hanging-punctuation) for headings
- Some way to collapse links so they are viewable but don't eat up lines. Maybe turn [link](https://example.org/this-is-a-really-long-url/see-how-it-keeps-going/very-long/) into this [link](…) with a tooltip?
- Syntax highlighting for code

The issue names no files, tests, or entry points. Start by locating the editable note component and its Markdown rendering or formatting code, then determine how the requested MVP features fit the existing editor. Done should be defined against the listed inline and block formatting behaviors, with polish items treated separately.

Written by the indexing model from the issue text.