Make canonical (sorted) strings from data

htlogr::data will now sort data by keys before assembling it all into
message so that order will not differ between invocations.

Added to both Perl and Python implementations.

lib/htlogr.pm

     carp("data must be a hash reference") unless ref $data == 'HASH';
 
     my @fields;
-    foreach (keys %$data) {
+    foreach (sort keys %$data) {
         push @fields, join $DIV_VALUE, $_, $data->$_;
     }
 

lib/htlogr.py

 
     def _serialize(self, data):
         fields = []
-        for key, value in data.iteritems():
+        for key in sorted(data.keys()):
+            value = data[key]
             fields.append("%s%s%s" % (key, self.DIV_VALUE, value))
         return self.DIV_FIELD.join(fields)