Remove "folding paper" styles from main element

[andrewjrhill]

Scope

Remove folding paper styles from the <main>...</main> page element.

Work Done

• Merged in changes recent changes from thespacedojo:crater-nova to bring branch up-to-date.
• Removed ::before psuedo element from _global.scss.
• Removed padding from sidebar from _sidebar.scss.
• Adjusted margin on .main{...} in _global.scss.
• Adjusted padding on .posts-item{...} in _posts.scss.
• Some minor spacing cleanup on _global.scss and _sidebar.scss.

Screenshots

@bengott
@queso