Enhance image type support (#18)

* adds tiff support

* doc update

* adds memory-based =IPixelariumImage= implementation

* add usage example for custom user control

* enhance

* clang-format

fix readme

fix docs

lib/imaging/impl/PixelariumMem.cpp

@@ -0,0 +1,26 @@
+#include "PixelariumMem.hpp"
+
+#include <filesystem>
+#include <memory>
+#include <opencv2/imgcodecs.hpp>
+#include <string>
+
+pixelarium::imaging::PixelariumMem::PixelariumMem(const cv::Mat& img, const std::string& name, const Log& log)
+    : img_(img), log_(log), name_(name)
+{
+    this->is_empty_ = false;
+    this->uri_ = std::filesystem::path();
+}
+
+std::unique_ptr<cv::Mat> pixelarium::imaging::PixelariumMem::TryGetImage()
+{
+    // ToDo: this craving for a revision of the whole concept:
+    // the interface requires a unique_ptr here. This concept was designed to "create an in-memory image on demand" sort
+    // of.
+    // I.e., it only makes sense for the file types that do not already manage a cv::Mat in memory.
+    // PixelariumMem is meant for exactly this in-memory management of a cv::Mat though.
+    // So, returning a unique_ptr from it in the following semantic essentially calls the
+    // copy constructor of cv::Mat. This is potentially not "super bad", but at least it requires attention at some
+    // point.
+    return std::make_unique<cv::Mat>(this->img_);
+}