Windows: correct tablet stylus rotation to range -180..180 degrees

When the user holds the Wacom Art Pen straight, rotation is zero;
when turning it counter-clockwise, it should have a negative angle,
whereas the driver sends a positive angle multiplied by 10;
when turning it clockwise it should have a positive angle up to 180,
whereas the driver sends 360 * 10 going downwards towards 180 * 10.
These corrections make the angle reading the same between Linux and
Windows.

Task-number: QTBUG-39570
Change-Id: I9f18ef6629bffa849c8d65cba02d42b21469cebc
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
add buttons to QTabletEvent

Until now, it has been necessary for tablet-oriented applications which
care about multi-button styli to reject each tablet event and wait for
the mouse event in order to know which buttons are pressed.  This patch
adds the new API and also the X11/xcb implementation.

[ChangeLog][QtCore][Tablet support] Added buttons to QTabletEvent

Task-number: QTBUG-39458
Change-Id: If2c9ec1ceacc1700a82686c5fc6f568f9111055a
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Windows: Streamline rawfont-lookup code.

Fix ugly warnings by MinGW:

qwindowsfontdatabase.cpp: In member function '{anonymous}::TableDirectory*
{anonymous}::EmbeddedFont::tableDirectoryEntry(const QByteArray&)':qwindowsfontdatabase.cpp:167:42: warning: comparison between signed and unsigned  integer expressions [-Wsign-compare]
         if (Q_UNLIKELY(m_fontData.size() < sizeof(OffsetSubTable)))
                                          ^
..\..\..\..\include/QtCore/../../src/corelib/global/qcompilerdetection.h:202:49:
 note: in definition of macro 'Q_UNLIKELY'

Change-Id: I47fac598ed1b6623146fb437c00da64d8e8b6984
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
QTabletEvent documentation improvements

Recent patches have added new functionality, and other aspects of the
documentation have been outdated for some time.

Task-number: QTBUG-39458
Change-Id: Ib7013eee091ff443971485133a58785d9284bc3d
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>