comply with html standards

image/x-icon is not a valid MIME type. the valid MIME for ico files is image/vnd.microsoft.icon.
the .ico file also contained 3 sizes (which we don't really need), which were poorly resized. One of the sizes actually had glitches, see https://i.imgur.com/OGWpggH.png

the /favicon.ico file remains, but contains only 1 image. The link/icon meta tag complies with the standard defined at
https://html.spec.whatwg.org/multipage/semantics.html#rel-icon. It links to favicon.png using image/png.

The ico file has been compressed to 1.1KB and the PNG is 0.5KB.

views/layout.jade

@@ -3,7 +3,7 @@ html
   head
     title= title
     link(rel='stylesheet', href='/stylesheets/style.css')
-    link(rel="icon", type="image/x-icon", href="/favicon.ico")
+    link(rel="icon", sizes="16x16", type="image/png", href="/favicon.png")
     link(href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.0/css/bootstrap.min.css", rel="stylesheet")
     link(name="description" content="A Minecraft avatar service with UUID support")
     link(name="keywords" content="minecraft, avatar, uuid")