Feature/read more text option

Quick fix to get our shortcodes up and running smoothly :) Also I gave the user an option (accessible via Admin with a checkbox similar to the other options) to add a "read more" text option for each post. For the sake of keeping things super minimal, the text content isn't readily customizable via Admin, but it is wrapped in a span with class .neatly--read-more, so it can technically be tweaked with CSS pseudo-selectors (appending an ellipsis, for example).