Normalize Article Typography

Article paragraphs have font-size: 15px, line-height: 24px, and font-weight: 300. But emphasized text has font-size: 14px and ordered list items have font-size: 13px and line-height: 18px.

These discrepancies look strange to me. This commit normalizes font-size, line-height, and font-weight in article paragraph and list text. It also makes emphasized text the same size as surrounding text (though <em>'s font-weight:400 has been preserved)