-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/sdlstdinc.d

@@ -0,0 +1,42 @@
+
+//          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.sdlstdinc;
+
+import bindbc.sdl.config;
+
+enum SDL_bool {
+    SDL_FALSE = 0,
+    SDL_TRUE = 1
+}
+
+mixin(expandEnum!SDL_bool);
+
+alias Sint8 = byte;
+alias Uint8 = ubyte;
+alias Sint16 = short;
+alias Uint16 = ushort;
+alias Sint32 = int;
+alias Uint32 = uint;
+alias Sint64 = long;
+alias Uint64 = ulong;
+
+enum SDL_FOURCC(char A, char B, char C, char D)  = ((A << 0) | (B << 8) | (C << 16) | (D << 24));
+
+version(BindSDL_Static) {
+    extern(C) @nogc nothrow {
+        void SDL_free(void* mem);
+    }
+}
+else {
+    extern(C) @nogc nothrow {
+        alias pSDL_free = void function(void* mem);
+    }
+
+    __gshared {
+        pSDL_free SDL_free;
+    }
+}