Fix the creaderasync example name in the qdoc file

This change eliminates the following warnings when using "make docs":

/home/lpapp/Projects/qt/qt5/qtserialport/examples/serialport/doc/creaderasync.qdoc:28:
warning: Cannot find file 'creader/creader.pro' or 'creader/creader.qmlproject'

/home/lpapp/Projects/qt/qt5/qtserialport/examples/serialport/doc/creaderasync.qdoc:28:
warning:   EXAMPLE PATH DOES NOT EXIST: creader

It is also visible that the example is unreachable on the following
documentation page:

http://qt-project.org/doc/qt-5/examples.html

Change-Id: I09f1532fcff6b1f7bfc5c4857bd14252aceb2eb3
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Refactor the reference in the documentation for property setters/getters

The documentation contains broken links due to this, and it is also inconsistent
with the rest. Properties should be referred to as properties, not individual
methods like setter, getter, notified signal, etc.

The change is tested with "make docs" and the broken links are history.

Change-Id: Id94cba1f88503754318c865793229e3d3947bec6
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>