Document missing QLatin1String methods

Most of them were added before 5.0, but it's ok to just list as 5.0.

Change-Id: I6e83a210a0165659f710d47ed595e9e89d5dbac9
Reviewed-by: Martin Smith <martin.smith@digia.com>
Initialize member.

Change-Id: I9ed8d5a7aeb40886bafbd9eb2003e88e5d796cc9
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>