Readable Bootstrap

[samozzy]

Use @extend to make the classes for rows and columns a bit more readable for non-Bootstrap users.

[samozzy]

Alternative, or additionally, use shortcodes for the same purpose (e.g., {{ 4col }} should wrap each item in
<div class="row"><div class="col-xs-4"> item </div></div>
Just relies on the user actually putting 4 things in...

[samozzy]

And also make clean-blog more DRY. Too many instances of col-md-4, col-lg-4, and similar.