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/libimhex/include/hex.hpp

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <cstdint>
+#include <cstddef>
+
+using u8    = std::uint8_t;
+using u16   = std::uint16_t;
+using u32   = std::uint32_t;
+using u64   = std::uint64_t;
+using u128  = __uint128_t;
+
+using s8    = std::int8_t;
+using s16   = std::int16_t;
+using s32   = std::int32_t;
+using s64   = std::int64_t;
+using s128  = __int128_t;
+
+extern int mainArgc;
+extern char **mainArgv;
+
+#define IMHEX_PLUGIN    namespace hex::plugin::internal {               \
+                            void setImGuiContext(ImGuiContext *ctx) {   \
+                                ImGui::SetCurrentContext(ctx);          \
+                            }                                           \
+                        }                                               \
+                        namespace hex::plugin
+
+#ifdef OS_WINDOWS
+#define MAGIC_PATH_SEPARATOR	";"
+#else
+#define MAGIC_PATH_SEPARATOR	":"
+#endif