Add conversion methods similar to those in QString to QByteArray. This
is often more useful than the QString version since std::string like
QByteArray are byte arrays.
[ChangeLog][QtCore][QByteArray] Added convenience methods to convert
directly to and from std::string.
Change-Id: I92c29d4bb1d9e06a667dd9cdd936970e2d272006
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>