html.py,style.css: use <pre> with no top-margin on all descriptions

After my last change dealing with this issue, I noticed that descriptions
with <pre> had an extra blank line at the top. Adding top-margin to the
CSS file made this go away, but it also made the <br/> superfluous. Thus,
it is simpler just to have every description use <pre> instead of <br/>.

This should finally resolve everything having to do with the add-on
descriptions.

If I'd noticed that the re module hadn't been imported, I probably wouldn't
have considered URL linking to be important enough to do so. Since I've
already written the code, however, I'll keep it.

data/tools/addon_manager/html.py

@@ -139,9 +139,7 @@ def w(x):
         if described != "(no description)":
             described = re.sub(r'(?<![">])http://[\w./?&=%~-]+', r'<a href="\g<0>">\g<0></a>', described)
             described = re.sub(r'(?<![\w>"/])(forums?|r|R|wiki)\.wesnoth\.org[\w./?&=%~-]+', r'<a href="http://\g<0>">\g<0>"</a>"', described)
-            if "\n" in described:
-                described = "<pre>" + described + "</pre>"
-        w('<div class="desc"><b>%s</b><br/>%s</div></td>' % (
+        w('<div class="desc"><b>%s</b><pre>%s</pre></div></td>' % (
             name, described))
         w("<td><b>%s</b><br/>" % name)
         w("Version: %s<br/>" % v("version", "unknown"))

data/tools/addon_manager/style.css

@@ -95,7 +95,8 @@ pre {
     white-space: -pre-wrap;      /* Opera 4-6 */
     white-space: -o-pre-wrap;    /* Opera 7 */
     word-wrap: break-word;       /* Internet Explorer 5.5+ */
-    font: inherit
+    font: inherit;
+    margin-top: 0;
 }
 
 /* tables */