-improved WASM compilation scripts

-added external bindbc.sdl import for WASM
-working on demos (WIP, working simple demo with ECS and SDL2)
-small change in ecs.std

demos/external/imports/bindbc/sdl/bind/sdlloadso.d

@@ -0,0 +1,28 @@
+
+//          Copyright Michael D. Parker 2018.
+// Distributed under the Boost Software License, Version 1.0.
+//    (See accompanying file LICENSE_1_0.txt or copy at
+//          http://www.boost.org/LICENSE_1_0.txt)
+
+module bindbc.sdl.bind.sdlloadso;
+
+version(BindSDL_Static){
+    extern(C) @nogc nothrow {
+        void* SDL_LoadObject(const(char)*);
+        void* SDL_LoadFunction(void*,const(char*));
+        void SDL_UnloadObject(void*);
+    }
+}
+else {
+    extern(C) @nogc nothrow {
+        alias pSDL_LoadObject = void* function(const(char)*);
+        alias pSDL_LoadFunction = void* function(void*,const(char*));
+        alias pSDL_UnloadObject = void function(void*);
+    }
+
+    __gshared {
+        pSDL_LoadObject SDL_LoadObject;
+        pSDL_LoadFunction SDL_LoadFunction;
+        pSDL_UnloadObject SDL_UnloadObject;
+    }
+}