Re-organize SASS structure (#1425)

sass/base/typography/_copy.scss

@@ -0,0 +1,53 @@
+p {
+	margin-bottom: 1.5em;
+}
+
+dfn,
+cite,
+em,
+i {
+	font-style: italic;
+}
+
+blockquote {
+	margin: 0 1.5em;
+}
+
+address {
+	margin: 0 0 1.5em;
+}
+
+pre {
+	background: $color__background-pre;
+	font-family: $font__pre;
+	font-size: 0.9375rem;
+	line-height: $font__line-height-pre;
+	margin-bottom: 1.6em;
+	max-width: 100%;
+	overflow: auto;
+	padding: 1.6em;
+}
+
+code,
+kbd,
+tt,
+var {
+	font-family: $font__code;
+	font-size: 0.9375rem;
+}
+
+abbr,
+acronym {
+	border-bottom: 1px dotted $color__border-abbr;
+	cursor: help;
+}
+
+mark,
+ins {
+	background: $color__background-ins;
+	text-decoration: none;
+}
+
+big {
+	font-size: 125%;
+}

sass/base/typography/_headings.scss

@@ -0,0 +1,8 @@
+h1,
+h2,
+h3,
+h4,
+h5,
+h6 {
+	clear: both;
+}

sass/base/typography/_typography.scss

@@ -0,0 +1,14 @@
+body,
+button,
+input,
+select,
+optgroup,
+textarea {
+	color: $color__text-main;
+	font-family: $font__main;
+	font-size: 1rem;
+	line-height: $font__line-height-body;
+}
+
+@import "headings";
+@import "copy";