Added Emmet cheatsheet (#737)

* Added Emmet cheatsheet

* Oops, forgot prism_lanugages property

emmet.md

@@ -0,0 +1,175 @@
+---
+title: Emmet
+category: Markup
+layout: 2017/sheet
+prism_languages: [html]
+---
+
+### Child: >
+
+```
+nav>ul>li
+```
+Expands to
+```html
+<nav>
+  <ul>
+    <li></li>
+  </ul>
+</nav>
+```
+
+
+### Sibling: +
+
+```
+section>p+p+p
+```
+Expands to
+```html
+<section>
+  <p></p>
+  <p></p>
+  <p></p>
+</section>
+```
+
+### Climb Up: ^
+
+```
+section>header>h1^footer
+```
+Expands to
+```html
+<section>
+  <header>
+    <h1></h1>
+  </header>
+  <footer></footer>
+</section>
+```
+
+### Grouping: ()
+
+```
+section>(header>nav>ul>li)+footer>p
+```
+Expands to
+```html
+<section>
+  <header>
+    <nav>
+      <ul>
+        <li></li>
+      </ul>
+    </nav>
+  </header>
+  <footer>
+    <p></p>
+  </footer>
+</section>
+```
+
+### Multiplication: \*
+
+```
+ul>li*3
+```
+Expands to
+```html
+<ul>
+  <li></li>
+  <li></li>
+  <li></li>
+</ul>
+```
+
+### IDs and Classes: . #
+
+```
+ul.menu>li.menu__item+li#id_item+li.menu__item#id_2
+```
+Expands to
+```html
+<ul>
+  <li class="menu__item"></li>
+  <li id="id_item"></li>
+  <li class="menu__item" id="id_2"></li>
+</ul>
+```
+
+### Numbering: $
+
+```
+ul>li.item$*3
+ul>li.item$$*3
+ul>li.item$@-*3
+ul>li.item$@3*5
+```
+Expands to
+```html
+<ul>
+  <li class="item1"></li>
+  <li class="item2"></li>
+  <li class="item3"></li>
+</ul>
+<ul>
+  <li class="item01"></li>
+  <li class="item02"></li>
+  <li class="item03"></li>
+</ul>
+<ul>
+  <li class="item3"></li>
+  <li class="item2"></li>
+  <li class="item1"></li>
+</ul>
+<ul>
+  <li class="item3"></li>
+  <li class="item4"></li>
+  <li class="item5"></li>
+</ul>
+```
+
+### Attributes: []
+
+```
+input[type="text"]
+div[data-attr="test"]
+```
+Expands to
+```html
+<input type="text" />
+<div data-attr="test"></div>
+```
+
+### Text: {}
+
+```
+p{Lorem ipsum}
+```
+Expands to
+```html
+<p>Lorem ipsum</p>
+```
+
+### Implicit tags
+
+```
+.default-block
+em>.default-inline
+ul>.default-list
+table>.default-table-row>.default-table-column
+```
+Expands to
+```html
+<div class="default-block"></div>
+<em><span class="default-inline"></span></em>
+<ul>
+  <li class="default-list"></li>
+</ul>
+<table>
+  <tr class="default-table-row">
+    <td class="default-table-column"></td>
+  </tr>
+</table>
+```