[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/12286] Add note that goto should not be used

PHPBB3-12286
[ticket/12286] Fix nesting of ul inside li element

PHPBB3-12286
[ticket/12286] Correctly capitalize PHP

PHPBB3-12286
[ticket/12286] Fix spelling of elephant(s) in the sample

PHPBB3-12286
[ticket/12286] Reword section about plurals

PHPBB3-12286
Merge remote-tracking branch 'github-nickvergessen/ticket/12286' into develop-ascraeus

* github-nickvergessen/ticket/12286:
  [ticket/12286] Reword section about plurals
  [ticket/12286] Fix spelling of elephant(s) in the sample
  [ticket/12286] Correctly capitalize PHP
  [ticket/12286] Fix nesting of ul inside li element
  [ticket/12286] Add note that goto should not be used
  [ticket/12286] Add section about plurals to the coding guidelines
  [ticket/12286] Classes must use the name space
  [ticket/12286] Remove section about utf8_normalize_nfc()
  [ticket/12286] Use $request->variable() instead of request_var()
  [ticket/12286] Function names should be prefixed with phpbb_
  [ticket/12286] Add "Since" to template event docs
  [ticket/12286] style.php and imagesets dont exist anymore
  [ticket/12286] Styles have a phpbb_version and a style_version in 3.1
  [ticket/12286] Use UTF8 (c) in style.cfg samples