Add plugin support

[jschmidt42]

Minimal example (test1.cpp)

#include <api.h>

static api_interface_t* api = nullptr;

static void minimal_plugin_menu(void* context)
{
    api->log->info(0, STRING_CONST("Hello World!"));
}

FRAMEWORK_API_EXPORT int load_plugin(api_plugin_context_t* plugin)
{
    // Initialize plugin info (optional)
    plugin->version_major = 1; plugin->version_minor = 0;
    string_copy(STRING_BUFFER(plugin->name), STRING_CONST("test1"));

    // Load API interface
    plugin->initialize_apis(plugin, &api);

    // Use the API to do things
    api->app->register_menu(STRING_CONST("Plugins/test1"), nullptr, 0, AppMenuFlags::None, minimal_plugin_menu, nullptr);

    return 0; // Everything's fine
}

FRAMEWORK_API_EXPORT void unload_plugin()
{
	// unload_plugin is optional is nothing special is required
}