Refactor notionBlockToMarkdown function

[LandonSchropp]

This pull request wholely refactors the notionBlockToMarkdown function.

Description

This code makes a few changes to the existing functionality:

• The reduce function could be removed by relying on the recursive nature of the blocks.
• Ensures that most block elements are always separated by two newlines. This is important to prevent them from being interpreted as a single entry, such as with back-to-back blockquotes.
• Allows blockquotes to contain child blocks, such as lists and paragraphs.
• Allows list items to contain child blocks, such as lists and paragraphs.

Motivation and Context

Originally, my motivation for this was that I needed a blockquote that could contain multiple paragraphs. However, I realized that my approach fixed a few other problems, so I went ahead and did the whole thing.

Screenshots

I created a test page in Notion to check the code.

So far, this seems to be parsing well! Here's what the generated markdown looks like:

This is an example paragraph.

[This](http://example.com) `is` **another** _example_ ~~paragraph~~.

---

## Header 1

### Header 2

#### Header 3

---
- [ ]  To do item 1
- [x]  To do item 2
  
  Child of to-do item 2
- [ ]  To do item 3
  
  - [x]  Child 1 of to-do item 3
  - [ ]  Child 2 of to-do item 3

---
* Bulleted item 1
* Bulleted item 2
  
  Child of bulleted item 2
* Bulleted item 3
  
  * Child 1 of bulleted item 3
  * Child 2 of bulleted item 3

---
1. Numbered item 1
1. Numbered item 2
  
  1. Child of numbered item 2
1. Numbered item 3
  
  1. Child 1 of numbered item 3
  1. Child 2 of numbered item 3

---

<details><summary>This is a toggle.</summary>This is the toggle content</details>

---

`` javascript [Backticks edited to display correctly on GitHub]
function() {
  return "code block";
}
``


---

![Bill Murray](https://s3.us-west-2.amazonaws.com/secure.notion-static.com/…1cd0dfe80051a2bc49a5&X-Amz-SignedHeaders=host&x-id=GetObject)

---

> I’m not superstitious, but I am a little stitious.
> 
> —Michael Scott (Steve Carrell),
> 
> _The Office_
---

<audio controls><source src="https://s3.us-west-2.amazonaws.com/secure.notion-static.com/…fe9bf0d1097063f19091&X-Amz-SignedHeaders=host&x-id=GetObject" /></audio>

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Security fix (non-breaking change wich fixes a security issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as
  expected)

[LandonSchropp]

Please let me know if there's anything else I can do. Thanks!

[orlowdev]

This is looking great! Thank you. I couldn't find the time to get back to refactoring this for half a year now.

[LandonSchropp]

Thank you!