[ticket/7707] Add get_username_string() where possible

PHPBB3-7707
[ticket/12286] Use UTF8 (c) in style.cfg samples

PHPBB3-12286
[ticket/12286] Styles have a phpbb_version and a style_version in 3.1

PHPBB3-12286
[ticket/12286] style.php and imagesets dont exist anymore

PHPBB3-12286
[ticket/12286] Add "Since" to template event docs

PHPBB3-12286
[ticket/12286] Function names should be prefixed with phpbb_

PHPBB3-12286
[ticket/12286] Use $request->variable() instead of request_var()

PHPBB3-12286
[ticket/12286] Remove section about utf8_normalize_nfc()

The request class takes care of this

PHPBB3-12286
[ticket/12286] Classes must use the name space

PHPBB3-12286
[ticket/12286] Add section about plurals to the coding guidelines

PHPBB3-12286
[ticket/11959] Use plurals for the language strings.

PHPBB3-11959
[ticket/11959] Fix the NOTIFICATION_QUOTE_TRIMMED text.

PHPBB3-11959
[ticket/11959] Use the plurals system for the untrimmed language strings.

PHPBB3-11959
[ticket/11959] List the last user with "and" instead of a comma.

PHPBB3-11959
[ticket/11959] Add samples for the untrimmed strings.

PHPBB3-11959
[ticket/11959] Add function to create a string list.

PHPBB3-11959
[ticket/11959] Simplify how the users are trimmed.

PHPBB3-11959
[ticket/11959] Rename phpbb_gen_string_list() & fix incorrect var name.

PHPBB3-11959
[ticket/11959] Remove use of plurals and make it possible to use Oxford comma.

PHPBB3-11959
[ticket/11959] Add unit tests.

PHPBB3-11959