[IMP] doc: simpler coding: utf-8

According to PEP-263, the -*- is just a variant "using formats recognized by
popular editors".

doc/reference/guidelines.rst

@@ -271,7 +271,7 @@ Idioms
 - Always favor *Readability* over *conciseness* or using the language features or idioms.
 - Use list comprehension, dict comprehension, and basic manipulation using ``map``, ``filter``, ``sum``, ... They make the code easier to read.
 - The same applies for recordset methods : use ``filtered``, ``mapped``, ``sorted``, ...
-- Each python file should have ``# -*- coding: utf-8 -*-`` as first line
+- Each python file should have ``# coding: utf-8 `` as first line
 - Use the ``UserError`` defined in ``openerp.exceptions`` instead of overriding ``Warning``, or find a more appropriate exception in *exceptions.py*
 - Document your code (docstring on methods, simple comments for the tricky part of the code)
 - Use meaningful variable/class/method names