Added Plugin support (#102)

* Build refactoring and initial plugin support

* Possibly fixed linux / mac build

* Added libdl to libglad build script

* Add glfw to imgui dependencies

* Refactored common functionality into "libimhex" for plugins

* Added plugin loading and example plugin

* Added proper API for creating a custom view and a custom tools entry with plugins

plugins/example/source/plugin_example.cpp

@@ -0,0 +1,33 @@
+#include <hex.hpp>
+
+#include <views/view.hpp>
+#include <imgui.h>
+
+class ViewExample : public hex::View {
+public:
+    ViewExample() : hex::View("Example") {}
+    ~ViewExample() override {}
+
+    void drawContent() override {
+        if (ImGui::Begin("Example")) {
+            ImGui::Text("Custom plugin window");
+        }
+        ImGui::End();
+    }
+};
+
+IMHEX_PLUGIN {
+
+    View* createView() {
+        return new ViewExample();
+    }
+
+    void drawToolsEntry() {
+        if (ImGui::CollapsingHeader("Example Tool")) {
+            ImGui::Text("Custom Plugin tool");
+        }
+    }
+
+}
+
+