Create `scss-docs` shortcode to get some snippets from the Scss source files

Created by: MartijnCuppens

This should be a little bit easier that creating a custom regex per case.

Usage in .scss:

// scss-docs-start awesome-code
.my-awesome-code {
  // The best CSS in the world
}
// scss-docs-end awesome-code

In the docs files:

{{< scss-docs name="awesome-code" file="scss/_variables.scss" >}}

I don't think the positive lookbehind syntax works in Hugo, so I replaced the comments in the end of the file, there are probably better ways to fix this (bump @XhmikosR)

TODO:

• Check all occurrences of code snippets
• Strip !default flags by default