docs: break longer text into paragraphs in HTML

Libvirt's HTML documentation is not as easy to the eyes as it could
be since long text has no visual breaks.

Take advantage of the formatting in documentation comments and wrap
each part separated by two consecutive \n into a HTML <p> element.

docs/newapi.xsl

@@ -83,6 +83,38 @@
     </xsl:for-each>
   </xsl:template>
 
+  <xsl:template name="formattext">
+    <xsl:param name="text" />
+
+    <xsl:if test="$text">
+      <xsl:variable name="head" select="substring-before($text, '&#xA;&#xA;')"/>
+      <xsl:variable name="rest" select="substring-after($text, '&#xA;&#xA;')"/>
+
+      <xsl:choose>
+        <xsl:when test="$head">
+          <p>
+            <xsl:call-template name="dumptext">
+              <xsl:with-param name="text" select="$head"/>
+            </xsl:call-template>
+          </p>
+        </xsl:when>
+        <xsl:when test="not($rest)">
+          <p>
+            <xsl:call-template name="dumptext">
+              <xsl:with-param name="text" select="$text"/>
+            </xsl:call-template>
+          </p>
+        </xsl:when>
+      </xsl:choose>
+
+      <xsl:if test="$rest">
+        <xsl:call-template name="formattext">
+          <xsl:with-param name="text" select="$rest"/>
+        </xsl:call-template>
+      </xsl:if>
+    </xsl:if>
+  </xsl:template>
+
   <xsl:template match="macro" mode="toc">
     <xsl:text>#define </xsl:text>
     <a href="#{@name}"><xsl:value-of select="@name"/></a>
@@ -254,11 +286,11 @@
     <xsl:variable name="name" select="string(@name)"/>
     <h3><a name="{$name}"><code><xsl:value-of select="$name"/></code></a></h3>
     <pre><xsl:text>#define </xsl:text><xsl:value-of select="$name"/></pre>
-    <p>
-    <xsl:call-template name="dumptext">
+    <div>
+    <xsl:call-template name="formattext">
       <xsl:with-param name="text" select="info"/>
     </xsl:call-template>
-    </p><xsl:text>
+    </div><xsl:text>
 </xsl:text>
   </xsl:template>
 
@@ -393,11 +425,11 @@
     <xsl:text>)
 </xsl:text>
     </pre>
-    <p>
-    <xsl:call-template name="dumptext">
+    <div>
+    <xsl:call-template name="formattext">
       <xsl:with-param name="text" select="info"/>
     </xsl:call-template>
-    </p>
+    </div>
     <xsl:if test="arg | return">
       <div class="variablelist"><table border="0"><col align="left"/><tbody>
       <xsl:for-each select="arg">
@@ -470,11 +502,11 @@
     <xsl:text>
 </xsl:text>
     </pre>
-    <p>
-    <xsl:call-template name="dumptext">
+    <div>
+    <xsl:call-template name="formattext">
       <xsl:with-param name="text" select="info"/>
     </xsl:call-template>
-    </p><xsl:text>
+    </div><xsl:text>
 </xsl:text>
     <xsl:if test="arg | return/@info">
       <div class="variablelist"><table border="0"><col align="left"/><tbody>