KaTeX website & documentation (#1484)

* website/docs: initial commit

* Change secondaryColor

* Fix index.css not being copied and included on global stylesheet

* Fix stylesheet link

[skip ci]

* Change documentation link to API(Usage)

[skip ci]

* Add `Libraries` in usage

[skip ci]

* Remove documentation from `README.md` and add link to the site

[skip ci]

* Use KaTeX in the parent directory to build Markdown

[skip ci]

* Revise function support page. Avoid error msgs.

* General edit to function support page

website/pages/en/users.js

@@ -0,0 +1,49 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const React = require('react');
+
+const CompLibrary = require('../../core/CompLibrary.js');
+const Container = CompLibrary.Container;
+
+const siteConfig = require(process.cwd() + '/siteConfig.js');
+
+class Users extends React.Component {
+  render() {
+    if ((siteConfig.users || []).length === 0) {
+      return null;
+    }
+    const editUrl = siteConfig.repoUrl + '/edit/master/website/siteConfig.js';
+    const showcase = siteConfig.users.map((user, i) => {
+      return (
+        <a href={user.infoLink} key={i}>
+          <img src={user.image} alt={user.caption} title={user.caption} />
+        </a>
+      );
+    });
+
+    return (
+      <div className="mainContainer">
+        <Container padding={['bottom', 'top']}>
+          <div className="showcaseSection">
+            <div className="prose">
+              <h1>Who is Using KaTeX?</h1>
+              <p>KaTeX is used by many projects</p>
+            </div>
+            <div className="logos">{showcase}</div>
+            <p>Are you using KaTeX?</p>
+            <a href={editUrl} className="button">
+              Add your project
+            </a>
+          </div>
+        </Container>
+      </div>
+    );
+  }
+}
+
+module.exports = Users;