-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/package.d

@@ -0,0 +1,46 @@
+
+//          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;
+
+public
+import bindbc.sdl.bind.sdl,
+       bindbc.sdl.bind.sdlassert,
+       bindbc.sdl.bind.sdlaudio,
+       bindbc.sdl.bind.sdlblendmode,
+       bindbc.sdl.bind.sdlclipboard,
+       bindbc.sdl.bind.sdlcpuinfo,
+       bindbc.sdl.bind.sdlerror,
+       bindbc.sdl.bind.sdlevents,
+       bindbc.sdl.bind.sdlfilesystem,
+       bindbc.sdl.bind.sdlgamecontroller,
+       bindbc.sdl.bind.sdlgesture,
+       bindbc.sdl.bind.sdlhaptic,
+       bindbc.sdl.bind.sdlhints,
+       bindbc.sdl.bind.sdljoystick,
+       bindbc.sdl.bind.sdlkeyboard,
+       bindbc.sdl.bind.sdlkeycode,
+       bindbc.sdl.bind.sdlloadso,
+       bindbc.sdl.bind.sdllog,
+       bindbc.sdl.bind.sdlmessagebox,
+       bindbc.sdl.bind.sdlmouse,
+       bindbc.sdl.bind.sdlpixels,
+       bindbc.sdl.bind.sdlplatform,
+       bindbc.sdl.bind.sdlpower,
+       bindbc.sdl.bind.sdlrect,
+       bindbc.sdl.bind.sdlrender,
+       bindbc.sdl.bind.sdlrwops,
+       bindbc.sdl.bind.sdlscancode,
+       bindbc.sdl.bind.sdlshape,
+       bindbc.sdl.bind.sdlstdinc,
+       bindbc.sdl.bind.sdlsurface,
+       bindbc.sdl.bind.sdlsystem,
+       bindbc.sdl.bind.sdlsyswm,
+       bindbc.sdl.bind.sdltimer,
+       bindbc.sdl.bind.sdltouch,
+       bindbc.sdl.bind.sdlversion,
+       bindbc.sdl.bind.sdlvideo,
+       bindbc.sdl.bind.sdlvulkan;