Add support for an XSLT DSL

[lukaseder]

For very simple XSL transformations, it might be useful to implement a simple DSL that allows for constructing XSL templates on the fly:

stylesheet(
    template(
        match("book"),
        element("book",
            attribute("id", "{@id + 1}"),
            applyTemplates()
        )
    ),

    template(
        match("@*|*|processing-instruction()|comment()"),
        copy(
            applyTemplates(select("*|@*|text()|processing-instruction()|comment()"))
        )
    )
);

The above would roughly be equivalent to:

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:template match="book">
        <book id="{@id + 1}">
            <xsl:apply-templates/>
        </book>
    </xsl:template>

    <xsl:template match="@*|*|processing-instruction()|comment()">
        <xsl:copy>
            <xsl:apply-templates select="*|@*|text()|processing-instruction()|comment()"/>
        </xsl:copy>
    </xsl:template>
</xsl:stylesheet>

Possibly, the DSL could be generated from the XSL XSD