Merge pull request #1810 from nickvergessen/ticket/11031

Ticket/11031 Bring phpBB2 converter up to speed with 3.1 changes
Merge remote-tracking branch 'brunoais/ticket/11663' into develop

* brunoais/ticket/11663:
  [ticket/11663] Add the doc block about the parameters.
  [ticket/11663] Add the doc block about the return value.
  [ticket/11663] Make generate_text_for_storage return the errors.