Use pandoc as markdown processor

The trigger but not the actual reason for this replacement of `kramdown` with `pandoc` was a strange generation issue with `kramdown`'s latest release.

All recent articles failed to generate anything more than an empty page. A quick check of the resulting HTML for those articles offered nothing out of the ordinary. After taking a close look at the articles in question I narrowed the set of failing articles down to those containing footnotes - tangentially I only started using footnotes a couple of articles ago i.e. this explained this part of the issue.

Some debugging of `InputXSLT` offered the following problem: `Xerces-C` generated an error message and stopped processing XML inputs containing `nbsp` non-blocking space characters in the implementation of the `external-command` function. This change in `kramdown`'s output can be traced back to enhancement issue [399](gettalong/kramdown#399). Obviously this is not a problem in `kramdown` but an issue in the way this static site generator is wrapping HTML inputs.

This problem should be solvable by adding appropriate namespace and doctype declarations to the markdown-generated HTML output. Instead I opted to perform the change to `pandoc` I had already planned for quite some time.

The choice fell on `pandoc` as it offers some additional markdown features as well as allowing for conversion to a rich set of document formats. i.e. features like printing articles as PDF using LaTeX are trivial to implement if `pandoc` is the markdown processor of choice. Furthermore page compilation is noticeably faster using `pandoc`.

One might note that this switch only solved the original issue by coincidence: Should `pandoc` start to generate non-blocking space characters the same problem will occur. But I have hopes that such a change would be configurable via `pandoc`'s plethora of configuration options. As this static site generator assumes everything to be XHTML I see no reason why I should not continue to treat HTML inputs as XML.

utility/formatter.xsl

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <xsl:stylesheet
 	version="1.0"
+	xmlns="http://www.w3.org/1999/xhtml"
 	xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 	xmlns:xalan="http://xml.apache.org/xalan"
 	xmlns:InputXSLT="function.inputxslt.application"
@@ -76,8 +77,8 @@
 		<xsl:with-param name="source" select="code/text()"/>
 		<xsl:with-param name="language">
 			<xsl:choose>
-				<xsl:when test="code/@class">
-					<xsl:value-of select="substring(code/@class, 10, string-length(code/@class))"/>
+				<xsl:when test="@class">
+					<xsl:value-of select="@class"/>
 				</xsl:when>
 				<xsl:otherwise>
 					<xsl:text>txt</xsl:text>
@@ -87,9 +88,17 @@
 	</xsl:call-template>
 </xsl:template>
 
-<xsl:template match="script" mode="embellish">
+<xsl:template match="div[@class = 'figure']" mode="embellish">
+	<p>
+		<xsl:apply-templates select="img" mode="embellish"/>
+	</p>
+</xsl:template>
+
+<xsl:template match="div[@class = 'footnotes']/hr" mode="embellish"/>
+
+<xsl:template match="span[contains(@class, 'math')]" mode="embellish">
 	<xsl:choose>
-		<xsl:when test="contains(@type, 'mode=display')">
+		<xsl:when test="contains(@class, 'display')">
 			<p class="math">
 				<xsl:call-template name="math_highlighter">
 					<xsl:with-param name="source" select="text()"/>
@@ -102,7 +111,7 @@
 		<xsl:otherwise>
 			<span class="math">
 				<xsl:call-template name="math_highlighter">
-					<xsl:with-param name="source"    select="text()"/>
+					<xsl:with-param name="source" select="text()"/>
 				</xsl:call-template>
 			</span>
 		</xsl:otherwise>
@@ -114,7 +123,7 @@
 
 	<xsl:variable name="content">
 		<xsl:call-template name="plain_formatter">
-			<xsl:with-param name="format">kramdown</xsl:with-param>
+			<xsl:with-param name="format">pandoc -f markdown -t html --katex --no-highlight</xsl:with-param>
 			<xsl:with-param name="source" select="$source"/>
 		</xsl:call-template>
 	</xsl:variable>