-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/sdlclipboard.d

@@ -0,0 +1,31 @@
+
+//          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.sdlclipboard;
+
+import bindbc.sdl.config;
+import bindbc.sdl.bind.sdlstdinc : SDL_bool;
+
+version(BindSDL_Static) {
+    extern(C) @nogc nothrow {
+        int SDL_SetClipboardText(const(char)*);
+        char* SDL_GetClipboardText();
+        SDL_bool SDL_HasClipboardText();
+    }
+}
+else {
+    extern(C) @nogc nothrow {
+        alias pSDL_SetClipboardText = int function(const(char)*);
+        alias pSDL_GetClipboardText = char* function();
+        alias pSDL_HasClipboardText = SDL_bool function();
+    }
+
+    __gshared {
+        pSDL_SetClipboardText SDL_SetClipboardText;
+        pSDL_GetClipboardText SDL_GetClipboardText;
+        pSDL_HasClipboardText SDL_HasClipboardText;
+    }
+}