Add FLAC importing via dr_flac

src/MagnumPlugins/AnyAudioImporter/AnyImporter.cpp

@@ -53,6 +53,8 @@ void AnyImporter::doOpenFile(const std::string& filename) {
         plugin = "VorbisAudioImporter";
     else if(Utility::String::endsWith(filename, ".wav"))
         plugin = "WavAudioImporter";
+    else if(Utility::String::endsWith(filename, ".flac"))
+        plugin = "FlacAudioImporter";
     else {
         Error() << "Audio::AnyImporter::openFile(): cannot determine type of file" << filename;
         return;

src/MagnumPlugins/AnyAudioImporter/AnyImporter.h

@@ -68,6 +68,7 @@ Supported formats:
     `VorbisAudioImporter`
 -   WAV (`*.wav`), loaded with @ref WavImporter "WavAudioImporter" or any other
     plugin that provides it
+-   FLAC (`*.flac`), loaded with any plugin that provides `FlacAudioImporter`
 
 Only loading from files is supported.
 */