* Move AppPlatform_emscripten to the sdl directory

As pointed out by #82, the behavior before this commit is unintuitive.

build-wasm.bat

@@ -44,7 +44,7 @@ cmake --build .
 ::bundle
 echo * Copying bundle data over.
 copy reminecraftpe.* ..\dist
-copy ..\..\platforms\emscripten\wasm_shell.html ..\dist\reminecraftpe.html
+copy ..\..\platforms\sdl\wasm_shell.html ..\dist\reminecraftpe.html
 copy ..\..\thirdparty\coi-serviceworker\coi-serviceworker.min.js ..\dist
 
 ::for me only

platforms/sdl/CMakeLists.txt

@@ -33,7 +33,7 @@ if(EMSCRIPTEN)
 add_executable(reminecraftpe
     main.cpp
 	AppPlatform_sdlbase.cpp
-    ../emscripten/AppPlatform_emscripten.cpp
+    AppPlatform_emscripten.cpp
     ../openal/SoundSystemAL.cpp
 )
 else()

platforms/sdl/main.cpp

@@ -6,7 +6,7 @@
 #include "client/app/App.hpp"
 
 #if	  defined(__EMSCRIPTEN__)
-#include "../emscripten/AppPlatform_emscripten.hpp"
+#include "AppPlatform_emscripten.hpp"
 typedef AppPlatform_emscripten UsedAppPlatform;
 #else
 #include "AppPlatform_sdl.hpp"