-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/package.d

@@ -0,0 +1,18 @@
+
+//          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;
+
+public import bindbc.sdl.config,
+              bindbc.sdl.bind;
+
+version(BindSDL_Static) {}
+else public import bindbc.sdl.dynload;
+
+version(BindSDL_Image) public import bindbc.sdl.image;
+version(BindSDL_Mixer) public import bindbc.sdl.mixer;
+version(BindSDL_TTF) public import bindbc.sdl.ttf;
+