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