documentation of i18n: TAL tags for translation...

...done, in developers doc, according to agreement in
http://article.gmane.org/gmane.comp.bug-tracking.roundup.devel/2836

Author: Alexander Smishlajev

TODO.txt

@@ -1,7 +1,6 @@
 This file contains items that need doing before the next release:
 
 Required:
-- documentation of i18n: TAL tags for translation
 - implementing logging for roundup-server, including command-line switches
 - fix documentation referring to configuration (config.ini, mysql.txt and
   postgresql.txt)