Add a slight background noise (v0.2.2)

The background noise makes the document look more like it's written on
paper.

The noise images are provided by the noisy-uris project:
https://github.com/markdurrant/noisy-uris

To avoid making another HTTP request, the images are base64 encoded, and
`@extend` is used to avoid duplicating the images.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "noisy-uris"]
+	path = noisy-uris
+	url = git://github.com/markdurrant/noisy-uris.git

noisy-uris

@@ -0,0 +1 @@
+Subproject commit b5f2dd634eccf0dc153577f0a98dcca83fe06eff

styling.sass

@@ -1,12 +1,15 @@
-// version 0.2.1
+// version 0.2.2
 
 @import "normalize"
+@import "noisy-uris/sass_vars/base-noise-uris"
+@import "noisy-uris/sass_vars/dark-noise-uris"
+@import "noisy-uris/sass_vars/light-noise-uris"
 @import "//fonts.googleapis.com/css?family=Libre+Baskerville:400,400italic,700"
 @import "//fonts.googleapis.com/css?family=Source+Code+Pro:400,400italic,700,700italic"
 
 // colors
 
-$background: #EEE
+$background: #F8F8F8
 $foreground: #111
 $footnote-color: #666
 $indent-color: #BBB
@@ -15,10 +18,14 @@ $block-border-color: $rule-color
 $block-background: #DDD
 $table-rule-color: #222
 
+%background-noise
+  background-image: url($base-noise-005)
+
 // typography
 
 body
   font-family: "Libre Baskerville", Baskerville, Georgia, serif
+  @extend %background-noise
   background-color: $background
   color: $foreground
   @media (max-width: 400px)
@@ -186,7 +193,8 @@ a, a:link, a:visited, a:hover
 code
   font-family: "Source Code Pro", "Consolas", "Monaco", monospace
   font-size: 85%
-  background: $block-background
+  @extend %background-noise
+  background-color: $block-background
   border: 1px solid $block-border-color
   padding: 0px 0.15em 0px 0.15em
   -webkit-border-radius: 3px
@@ -238,10 +246,12 @@ tr
     font-weight: 700
 
   &.odd
-    background: #EEEEEE
+    @extend %background-noise
+    background-color: #EEEEEE
 
   &.even
-    background: #CCCCCC
+    @extend %background-noise
+    background-color: #CCCCCC
 
 tbody:last-child // last row
   border-bottom: 1px solid $table-rule-color
@@ -265,7 +275,8 @@ figure
   text-align: center
   padding: 0px
   width: 100%
-  background: $block-background
+  @extend %background-noise
+  background-color: $block-background
   border: 1px solid $block-border-color
   -webkit-border-radius: 8px
   -moz-border-radius: 8px