Add some styling to doc, improve top menu

* doc/snippet-expansion.org:
* doc/snippet-organization.org: Fix typos.
* doc/stylesheets/manual.css: Add some simple styling.  Mainly, this
sets 'max-width' for the main text, and centers it.  Adjust the
background color.
* doc/nav-menu.html.inc: Adjust 'class' of top menu.
* doc/yas-doc-helper.el (yas--make-preamble): New function, used for
:html-preamble.  It sets the element for the current page in the top
menu as bolded text to aid navigation.
* doc/stylesheets/styles.css: Remove, it was unused since the old rst
manual was removed.

doc/stylesheets/manual.css

@@ -1,5 +1,14 @@
-nav > ul > li.center > ul {
-    padding: 0;
+.center { margin-left: auto; margin-right: auto; text-align: center; }
+.current {
+    font-weight: bold;
+    background-color: #E0E8F0;
+}
+
+body { background-color:  #E4F0F4 }
+div#content {
+    max-width: 20cm;
+    margin-left: auto;
+    margin-right: auto;
 }
 
 nav li {
@@ -9,20 +18,22 @@ nav li {
     list-style-type: none;
     padding: 0.5em;
 }
-
 nav > ul > li {
     display: inline-block;
 }
-
-/* match org's css for <pre> */
-code {
-    background-color: #F3F5F7;
-    font-family: courier, monospace;
+.nopad {
+    padding: 0;
+}
+li.border {
+    border: solid;
+    border-width: 1px;
 }
 
-#content {
-    margin-left: 5%;
-    margin-right: 10%;
+pre, code{ background-color: #F3F5F7; }
+code {
+    /* http://neugierig.org/software/chromium/notes/2009/09/monospace-fonts-workaround.html */
+    font-family: WorkAroundWebKitAndMozilla, monospace;
+    white-space: nowrap;
 }
 
 /* Styles for htmlize.el fontification.  */

doc/stylesheets/styles.css

@@ -1,93 +0,0 @@
-@media all
-{
-    body {
-        margin: 1em auto;
-        /*margin: 10px 18% 10px 18%;*/
-        font-family: Arial;
-        /*text-align: justify;*/
-        font-size: 14pt;
-        padding: 10px;
-        line-height: 1.2em;
-        max-width: 600pt;
-    }
-
-    div#table-of-contents {
-        position: fixed;
-        left: 0%;
-        right: 0%;
-        top: 0px;
-        z-index: 100;
-        background: black;
-    }
-
-    div#table-of-contents h2 {
-        display: none;
-    }
-
-    div#table-of-contents a {
-        text-decoration: none;
-        color: white;
-    }
-
-    div#table-of-contents a:visited {
-        color: white;
-    }
-
-    div#table-of-contents a:hover {
-        color: orange;
-    }
-
-    div.outline-2 h2{
-        padding-top: 50px;
-    }
-
-    div#text-table-of-contents {
-        text-color: white;
-        text-align: center;
-        margin-left: 30%;
-        margin-right: 30%;
-    }
-
-    div#text-table-of-contents ul {
-        height: 2em;
-        width: 500px;
-        list-style: none;
-        margin: auto;
-    }
-
-    div#text-table-of-contents ul li {
-        float: left;
-        margin-left:auto;
-        margin-right: auto;
-        padding-left: 10px;
-    }
-
-    div#postamble{
-        position: fixed;
-        width: 800px;
-        height: 250px;
-        left: 50%;
-        right: 50%;
-        margin:-75px 0 0 -400px;
-        bottom: -20px;
-        font-size: 10pt;
-        color: grey;
-        background: url('siscog-bottom-logo.png') no-repeat;
-        /* background-size: 100% 100%; */
-    }
-
-    div#postamble *{
-        display: none;
-    }
-
-    div#postamble p.date{
-        position: relative;
-        bottom: -200px;
-        text-align: center;
-        display: block;
-    }
-
-
-
-
-}