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/app/rendering/RenderImageManager.cpp

@@ -46,9 +46,10 @@ bool pixelarium::application::RenderImageManager::Remove(resources::ResourceKey
 /// @return void.  No exception is thrown.
 void pixelarium::application::RenderImageManager::Add(resources::ResourceKey key) noexcept
 {
-    // we don't want to add what's already there
-    // or empty render images
-    if (this->render_image_map_.contains(key))
+    // we don't want to add what's already there, render empty images, or failed keys
+    if (this->render_image_map_.contains(key)
+        // || this->failed_keys_cache_.contains(key)
+    )
     {
         return;
     }
@@ -56,6 +57,8 @@ void pixelarium::application::RenderImageManager::Add(resources::ResourceKey key
     auto current_view = this->view_factory_->RenderImage(key);
     if (current_view == nullptr)
     {
+        // failed to create view, cache this key to avoid repeated attempts
+        this->failed_keys_cache_.insert(key);
         return;
     }