Update template files for texinfo documentation manuals:
- Stargin using =MANUAL_NAME= translation marker to dynamically
replace manual's name when new manuals are created.
- Add index inclusion inside manual.texinfo.
- Inside es_ES templates, stop using texinfo special way of print
special characters. This requires changing the terminal's
encoding from utf-8 to iso-8859-1 in order for those characters
to be printed correctly.