Fix build when fwrite() is declared with attribute warn_unused_result

Task-number: QTBUG-33921
Change-Id: I58dded1f54239e4c5cfd5f4f5c1655dbf879b2c8
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Add missing operators QMargins -=,+= (int).

Task-number: QTBUG-34079

Change-Id: If61cc01ba70345b01f13072769d3a38f23e8cefc
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Doc: Adding "\keyword Signals and Slots" to "Signals & Slots" page.

-many articles link to the page using the "and" or the "&"
version, causing missing links.

Change-Id: I6447149befce169cfafff29164172290a7c15f0c
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>