Update C++ style guide to 3.180:
 - Remove comment about naming macros like enums.
 - Move a bad code snippet from a CODE_SNIPPET to a BAD_CODE_SNIPPET element.

Update Python style guide to 2.18:
 - Clarify the syntax for import statements.

Update styleguide.xsl to 1.31:
 - Substitute underscore for apostrophe in anchor names.
diff --git a/styleguide.xsl b/styleguide.xsl
index e82e8f1..38345d5 100644
--- a/styleguide.xsl
+++ b/styleguide.xsl
@@ -449,7 +449,9 @@
        Substitutes underscore for characters unsuitable for URLs  -->
   <xsl:template name="anchorname">
     <xsl:param name="sectionname"/>
-    <xsl:value-of select="translate($sectionname,' ()#','____')"/>
+    <!-- strange quoting necessary to strip apostrophes -->
+    <xsl:variable name="bad_characters" select="&quot; ()#'&quot;"/>
+    <xsl:value-of select="translate($sectionname,$bad_characters,'_____')"/>
   </xsl:template>
 
   <!-- Given text, evaluates to the number of leading spaces. -->