build system and module refactoring + simple histogram scratch (#20)

* scratch adding histogram to image views

Histograms should come from some sort of histogram service. This is
currently just a POC.

* custom logger implementation w/o spdlog

* missing cmake file

* fix tests

* use operator<< over direct stream exposure

* rm print header

* add threading test + refactor towards interface libraries

omits the need for =target_include_directories= calls /everywhere/

* rm print header

* rm constexpr

* templated thread_pool

* fix doxyfile

* default enable doc building

* czi reader refactor

* rm erroneous include expression

* clang-format

* single lib include with PUBLIC visibility

* compile imgui stdlib

* clang format

* documentation update

centralize `LogLevelToString` to `ILog.hpp`

update docs and examples

lib/imaging/impl/include/PixelariumTiff.hpp

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <stdexcept>
+#include <string>
+
+#include "ILog.hpp"
+#include "IPixelariumImage.hpp"
+
+namespace pixelarium::imaging
+{
+/// @brief Implements support for .tiff-images in the realm of IPixelariumImage
+class PixelariumTiff : public IPixelariumImageCvMat
+{
+    using Log = pixelarium::utils::log::ILog;
+
+   public:
+    explicit PixelariumTiff(const std::string& uri, const Log& log);
+
+    // IPixelariumImage member implementations
+   public:
+    std::optional<cv::Mat> TryGetImage() override;
+
+    std::optional<cv::Mat> TryGetImage(const IImageQuery&) override
+    {
+        // ToDo: proper error
+        throw std::runtime_error("Not possible with tiff.");
+    }
+
+    std::vector<std::optional<cv::Mat>> TryGetImages(const IImageQuery&) override
+    {
+        // ToDo: proper error
+        throw std::runtime_error("Not possible with tiff.");
+    }
+
+    bool Empty() const noexcept override { return this->is_empty_; }
+
+   public:
+    const static ImageFileType type_{ImageFileType::kTiff};
+
+   private:
+    // this should be set by each image getter
+    // after a new cv::Mat could be instantiated
+    bool is_empty_{true};
+    const Log& log_;
+};
+}  // namespace pixelarium::imaging