Add OpenSearch support

Author: eksperimental

_includes/search.html

@@ -5,7 +5,7 @@ <h3>
 </div>
 
 <div class="widget search">
-  <form method="get" class="search-form" action="https://www.google.com/search">
+  <form method="get" id="search-form" class="search-form" action="https://www.google.com/search">
 		<div>
 			<input class="search-text" type="text" name="q" placeholder="Search..." id="searchfield">
 			<input type="hidden" name="sitesearch" value="elixir-lang.org">

_includes/top.html

@@ -14,6 +14,7 @@
   <meta name="viewport" content="width=device-width,initial-scale=1" />
   <link rel="stylesheet" id="font-bitter-css" href="http://fonts.googleapis.com/css?family=Bitter:400,700" type="text/css" media="screen" />
   <link rel="shortcut icon" type="image/x-icon" href="/favicon.ico" />
+  <link rel="search" type="application/opensearchdescription+xml" title="elixir-lang.org" href="/opensearch.xml" />
   <script>
   (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
   (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),

opensearch.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/"
+	xmlns:moz="http://www.mozilla.org/2006/browser/search/">
+  <Description>Search Elixir website</Description>
+  <SearchForm>http://elixir-lang.org/</SearchForm>
+  <moz:SearchForm>http://elixir-lang.org/</moz:SearchForm>
+  <InputEncoding>UTF-8</InputEncoding>
+  <Language>en</Language>
+
+  <ShortName>elixir-lang.org</ShortName>
+  <Url rel="self" type="application/opensearchdescription+xml" href="http://elixir-lang.org/opensearch.xml" />
+  <Url method="get" type="text/html" 
+      template="https://www.google.com/search?q={searchTerms}&amp;sitesearch=elixir-lang.org" />
+  <Image width="16" height="16">http://elixir-lang.org/favicon.ico</Image>
+</OpenSearchDescription>