code block copy to clipboard button

[cellcoresystems]

Is your feature request related to a problem? Please describe.
I really would love to have a copy to clipboard button on every code block on the upper right/left corner.

Describe the solution you'd like
For example :o)
prismjs - copy to clipbord
clipboardjs -smaller lightweight

Describe alternatives you've considered
From clipboardjs.com
A browser extension that adds a "copy to clipboard" button to every code block on GitHub, MDN, Gist, StackOverflow, StackExchange, npm, and even Medium.

Install for Chrome and Firefox.

[wft44maqb]

ping?

[joshlopes]

ping?

[tlambert03]

ping?

[AndrewHess]

Please add this soon. Or at least a way to manually enable it for certain code blocks

[planetoid]

參考別人的 user script 改了一版。

安裝方法：

1. 瀏覽器安裝 Tampermonkey (篡改猴) 擴充套件 https://www.tampermonkey.net/
2. 前往與安裝 HackMD Copy Code Snippet https://greasyfork.org/zh-TW/scripts/506037-hackmd-copy-code-snippet

已知 bug：如果在編輯模式，新增的程式碼區塊不會有 Copy 按鈕，需要重新載入網頁才會出現。