Create gist for each code block

I will modify the plugin so it creates a gist for each code block in markdown. I also want to anotate the language of the gist so I can do something like this:

``` scala
def someScalaFunction(x: Int) = x + 1
```

it should create a gist with _.scala_ extension so the code gets render with the Scala colors.

I also might one to insert the gist url below the code block. :)

The issue targets the MacDown plugin's handling of Markdown code blocks and gist creation. Start by locating those existing entry points and determine how the fenced language is represented, then confirm whether inserting a gist URL is part of the required scope. Done means each block produces a gist with the requested language extension and the agreed URL behavior is covered.

Written by the indexing model from the issue text.