External and internal audio players work similarly now. Fixes #950.
* inherit a new ExternalAudioPlayer class from AudioPlayerInterface;
* use an existing ExternalViewer class to implement ExternalAudioPlayer;
* take (const char *, int) instead of std::vector<char> in
ExternalViewer constructor to fit into AudioPlayerInterface;
* extend ExternalViewer API to let ExternalAudioPlayer stop superseded
audio player processes;
* make AudioPlayerInterface::play() return an error message string to
allow reporting immediate failures from derived classes;
* Document AudioPlayerInterface API;
* Document AudioPlayerFactory::player();
* use the common audio interface exclusively in ArticleView.
* add a new interface class AudioPlayerInterface;
* inherit a new proxy class Ffmpeg::AudioPlayer from it;
* partially switch ArlticleView to using the interface;
* expose MainWindow's AudioPlayerInterface instance to all ArticleView
instances;
* add a new AudioPlayerFactory class responsible for creating instances
of concrete classes derived from AudioPlayerInterface depending on
relevant Config::Preferences values;
* increase minimum supported Qt version from 4.5 to 4.6 in README
in order to use QScopedPointer introduced in Qt 4.6.
The result of a downcast to a wrong dynamic type is undefined according
to the C++ standard.
Wrong casts were detected at goldendict start by GCC's
-fsanitize=undefined option. This commit fixes #974.
Internal links in MediaWiki articles don't lead to word definitions,
so the "Definition: " prefix is not correct for them. It also does not
provide any information and is largely useless.
Perhaps the actual footnote text should be displayed in the tooltip,
but this requires distinguishing them from citations/references and
backlinks.