docs(header): replace logo.png with logo.svg

The current logo looks awful on high-density displays.  SVG is a
better choice because it can scale to any resolution without
increasing file size.

Amending #2775 to add support for IE 8 by falling back to existing PNG
with img.onerror

Using relative URLs as directed by @btford and @petebacondarwin.

(commit by Brenton Simpson - @appsforartists)

Closes #2874

Author: appsforartists

docs/img/angularjs-for-header-only.svg

@@ -1,3 +1,18 @@
+/* Logo */
+
+.header .brand {
+  padding-top: 6px;
+  padding-bottom: 0px;
+}
+
+.header .brand img {
+  height: 25px;
+  width: 92px;
+}
+
+/* end: Logo */
+
+
 /* this is here to avoid the display=block shuffling of ngShow */
 .breadcrumb li > * {
   float:left;
@@ -356,7 +371,7 @@ ul.events > li > h3 {
   opacity:1;
 }
 
-.popover-incode code, 
+.popover-incode code,
 .popover-incode pre {
   white-space:nowrap;
 }

docs/src/templates/css/docs.css

@@ -122,8 +122,8 @@
     <div class="navbar navbar-inverse navbar-fixed-top">
       <div class="navbar-inner">
         <div class="container">
-          <a class="brand" href="http://angularjs.org" style="padding-top: 6px; padding-bottom: 0;">
-            <img class="AngularJS-small" src="http://angularjs.org/img/AngularJS-small.png">
+          <a class="brand" href="http://angularjs.org">
+            <img class="logo" src="img/angularjs-for-header-only.svg">
           </a>
           <ul class="nav">
             <li class="divider-vertical"></li>
@@ -274,7 +274,7 @@ <h4>{{ key }}</h4>
                 <a href="{{page.url}}" tabindex="2">{{page.shortName}}</a>
               </li>
             </ul>
-            
+
             <ul class="nav nav-list well api-list-item" ng-repeat="module in modules track by module.url">
               <li class="nav-header module">
                 <a class="guide" href="{{URL.module}}">module</a>