Add documentation for image formats

Author: adazem009

Doxyfile

@@ -975,6 +975,7 @@ EXCLUDE_SYMLINKS       = NO
 
 EXCLUDE_PATTERNS       = */internal/* \
                          */src/blocks/* \
+                         */src/imageformats/* \
                          *_p.cpp \
                          *_p.h
 

docs/Image formats.md

@@ -0,0 +1,33 @@
+\page imageFormats Image formats
+
+To work with costumes, libscratchcpp has to read image files from Scratch projects.
+No formats are currently supported, but that will change soon.
+
+# Implementing a custom image format
+To implement a custom image format that libscratchcpp doesn't support,
+subclass \link libscratchcpp::IImageFormat IImageFormat \endlink
+and override all of the methods.
+
+Then subclass \link libscratchcpp::IImageFormatFactory IImageFormatFactory \endlink
+and override \link libscratchcpp::IImageFormatFactory::createInstance() createInstance() \endlink.
+
+It's recommended to use the libscratchcpp namespace like this in your classes:
+```cpp
+using namespace libscratchcpp;
+```
+
+Here's an example of the `createInstance()` method:
+```cpp
+std::shared_ptr<IImageFormat> TiffImageFormatFactory::createInstance() {
+    return std::make_shared<TiffImageFormat>();
+}
+```
+
+# Registering the image format
+To register the image format, you need to register the factory class.
+It will be used by classes such as \link libscratchcpp::Costume Costume \endlink
+internally to instantiate your image format.
+
+```cpp
+libscratchcpp::ScratchConfiguration::registerImageFormat("tiff", std::make_shared<TiffImageFormatFactory>());
+```