Markdown.pl: permit '#' suffix on backticks block language name

The language name specified for syntax highlighting generally has
to be composed of "word" characters (alphanumeric and "_") plus
"+", "-" and ".".

Allow a final trailing "#" on the language name so that c# and f#
can be used as language names.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>

Markdown.pl

@@ -646,7 +646,7 @@ sub _HashBTCodeBlocks {
 
     $text =~ s{
 	    (?:(?<=\n)|\A)
-		([ ]{0,$less_than_indent})``(`+)[ \t]*(?:([\w.+-]+)[ \t]*)?\n
+		([ ]{0,$less_than_indent})``(`+)[ \t]*(?:([\w.+-]+[#]?)[ \t]*)?\n
 	     ( # $4 = the code block -- one or more lines, starting with ```
 	      (?:
 		.*\n+