Create tech stack docs (techstack.yml and techstack.md)

[stack-file]

Adding tech stack documentation to allow anyone to easily see what is being used in this repo without digging through config files. Two files are being added: techstack.yml and techstack.md. techstack.yml contains data on all the technologies being used in this repo. techstack.md is a visualization of the YML file and displays the tech stack data in a pretty Markdown file.

💡 Protip: techstack.md contains a comment at the top of the file that the following README snippet (with and without the logos) at the top of the file as a comment:

<--- Readme.md Snippet without images Start --->

Tech Stack

dreamfactorysoftware/df-core is built on the following main stack:

• PHP – Languages
• Symfony – Frameworks (Full Stack)
• PHPUnit – Testing Frameworks
• Guzzle – Microframeworks (Backend)

Full tech stack here

<--- Readme.md Snippet without images End --->

Get the code:

## Tech Stack
dreamfactorysoftware/df-core is built on the following main stack:

- [PHP](http://www.php.net/) – Languages
- [Symfony](http://symfony.com/) – Frameworks (Full Stack)
- [PHPUnit](https://phpunit.de/) – Testing Frameworks
- [Guzzle](http://guzzlephp.org/) – Microframeworks (Backend)

Full tech stack [here](/techstack.md)

---

<--- Readme.md Snippet with images Start --->

Tech Stack

dreamfactorysoftware/df-core is built on the following main stack:

• PHP – Languages
• Symfony – Frameworks (Full Stack)
• PHPUnit – Testing Frameworks
• Guzzle – Microframeworks (Backend)

Full tech stack here

<--- Readme.md Snippet with images End --->

Get the code:

## Tech Stack
dreamfactorysoftware/df-core is built on the following main stack:

- <img width='25' height='25' src='https://img.stackshare.io/service/991/hwUcGZ41_400x400.jpg' alt='PHP'/> [PHP](http://www.php.net/) – Languages
- <img width='25' height='25' src='https://img.stackshare.io/service/1197/logosf_positif_03_icon.png' alt='Symfony'/> [Symfony](http://symfony.com/) – Frameworks (Full Stack)
- <img width='25' height='25' src='https://img.stackshare.io/service/1616/1_WsEnddd5Y4EgEHsT054kUQ.jpeg' alt='PHPUnit'/> [PHPUnit](https://phpunit.de/) – Testing Frameworks
- <img width='25' height='25' src='https://img.stackshare.io/service/2350/638632.png' alt='Guzzle'/> [Guzzle](http://guzzlephp.org/) – Microframeworks (Backend)

Full tech stack [here](/techstack.md)