-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/sdltimer.d

@@ -0,0 +1,51 @@
+
+//          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.sdltimer;
+
+import bindbc.sdl.bind.sdlstdinc : SDL_bool;
+
+extern(C) nothrow alias SDL_TimerCallback = uint function(uint interval, void* param);
+alias SDL_TimerID = int;
+
+// This was added to SDL 2.0.1 as a macro, but it's
+// useful & has no dependency on the library version,
+// so it's here for 2.0.0 as well.
+@nogc nothrow pure
+bool SDL_TICKS_PASSED(uint A, uint B) {
+    pragma(inline, true);
+    return cast(int)(B - A) <= 0;
+}
+
+version(BindSDL_Static) {
+    extern(C) @nogc nothrow {
+        uint SDL_GetTicks();
+        ulong SDL_GetPerformanceCounter();
+        ulong SDL_GetPerformanceFrequency();
+        void SDL_Delay(uint);
+        SDL_TimerID SDL_AddTimer(uint,SDL_TimerCallback,void*);
+        SDL_bool SDL_RemoveTimer(SDL_TimerID);
+    }
+}
+else {
+    extern(C) @nogc nothrow {
+        alias pSDL_GetTicks = uint function();
+        alias pSDL_GetPerformanceCounter = ulong function();
+        alias pSDL_GetPerformanceFrequency = ulong function();
+        alias pSDL_Delay = void function(uint);
+        alias pSDL_AddTimer = SDL_TimerID function(uint,SDL_TimerCallback,void*);
+        alias pSDL_RemoveTimer = SDL_bool function(SDL_TimerID);
+    }
+
+    __gshared {
+        pSDL_GetTicks SDL_GetTicks;
+        pSDL_GetPerformanceCounter SDL_GetPerformanceCounter;
+        pSDL_GetPerformanceFrequency SDL_GetPerformanceFrequency;
+        pSDL_Delay SDL_Delay;
+        pSDL_AddTimer SDL_AddTimer;
+        pSDL_RemoveTimer SDL_RemoveTimer;
+    }
+}