Docs: Update multiple pages to fix rendering of fenced code blocks

I first noticed a problem on the "Configuring ESLint" page (http://eslint.org/docs/configuring/ and search for "sharedData") - the lack of a blank line above the fenced code block resulted in incorrect rendering.

After making that change, I searched for other instances of the problem and found a few (though their rendering issues are generally more subtle). This commit makes sure all fenced code blocks in the documentation have a blank line before and after the ``` fence. (The line after seems less necessary and is there more for consistency.)

If you'd like any changes to the proposed commit, please let me know!