TGA: Support for TGA specification 2.0

Adds TGA 2.0 compliance:
- Support for Extension Area, Developer Area and Footer (metadata support)
- Support for 15-bit and 16-bit per pixel images (both RGB and Indexed)
- Full support for rotation on reading (we cannot use Qt transformations because only a subset is part of the TGA specification)
- When writing you can choose the supported version (subType)
- Improved writing speed (approximately 10 times) and removed whole image conversions (significant memory savings)

It pass the [TrueVision TGA 2.0 conformance suite](https://github.com/zigimg/test-suite/tree/master/fixtures/tga).

Test changes:
- Read test: added ability to skip a specific test on sequential devices (via JSON behavior file)
- Write test: added the ability to set the subType when writing (via JSON properties file)

Closes #37

src/imageformats/CMakeLists.txt

@@ -137,7 +137,7 @@ kimageformats_add_plugin(kimg_sct SOURCES sct.cpp)
 
 ##################################
 
-kimageformats_add_plugin(kimg_tga SOURCES tga.cpp)
+kimageformats_add_plugin(kimg_tga SOURCES tga.cpp microexif.cpp scanlineconverter.cpp)
 
 ##################################
 

src/imageformats/tga_p.h

@@ -22,17 +22,20 @@ public:
     bool write(const QImage &image) override;
 
     bool supportsOption(QImageIOHandler::ImageOption option) const override;
+    void setOption(ImageOption option, const QVariant &value) override;
     QVariant option(QImageIOHandler::ImageOption option) const override;
 
     static bool canRead(QIODevice *device);
 
 private:
     bool writeIndexed(const QImage &image);
-
     bool writeGrayscale(const QImage &image);
-
+    bool writeRGB555(const QImage &image);
     bool writeRGBA(const QImage &image);
 
+    bool writeMetadata(const QImage &image);
+    bool readMetadata(QImage &image);
+
     const QScopedPointer<TGAHandlerPrivate> d;
 };