Ticket/12286 Update Coding Guidelines

- Classes use namespaces now
- Most classes have been moved to phpbb/ instead of include/
- styles.php does not exist anymore
- Function names should be prefixed with phpbb_
- request_var() should not be used but $request->variable()
- style.cfg should not use html but uft8 (c)
- Styles should have style and phpbb version in their .cfg
- Template events are missing * Since line
- utf8_normalize_nfc() around requested utf8 variables is not needed (done by the class)
- Translation section should have a link to https://wiki.phpbb.com/Plural_Rules

http://tracker.phpbb.com/browse/PHPBB3-12286