fix: Move sourcecode classes (#839)

* Move sourcecode classes

The HTML elements created for a `<sourcecode>` element have class
attributes attached to the `<pre>` element.  In comparison, `<artwork>`
is rendered with class attributes attached to the outer `<div>`.

Having the classes on the outer `<div>` makes it a LOT easier to style
these properly, so I've moved them to this CL.

* Update CSS to match

* .breakable is also affected

xml2rfc/data/xml2rfc.css

@@ -617,7 +617,7 @@ hr.addr {
  figure {
  overflow: scroll;
  }
- pre.breakable {
+ .breakable pre {
  break-inside: auto;
  }
  h1, h2, h3, h4, h5, h6 {
@@ -792,7 +792,7 @@ tt, code, pre {
 }
 
 /* Fix the height/width aspect for ascii art*/
-pre.sourcecode,
+.sourcecode pre,
 .art-text pre {
  line-height: 1.12;
 }
@@ -1128,7 +1128,7 @@ dd > div.artwork:first-child,
 dd > aside:first-child,
 dd > figure:first-child,
 dd > ol:first-child,
-dd > div:first-child > pre.sourcecode,
+dd > div.sourcecode:first-child,
 dd > table:first-child,
 dd > ul:first-child {
  clear: left;

xml2rfc/writers/html.py

@@ -2469,9 +2469,9 @@ def render_sourcecode(self, h, x):
  classes += ' lang-%s' % type
  if (len(x.text.split('\n')) > 50):
  classes += ' breakable'
- div = add.div(h, x)
+ div = add.div(h, x, classes=classes)
  div.text = None
- pre = add.pre(div, None, x.text, classes=classes)
+ pre = add.pre(div, None, x.text)
  if mark:
  text = pre.text
  if file: