Update wasm instructions.

Also update the quotes in CMake following:
https://emscripten.org/docs/getting_started/FAQ.html#how-do-i-specify-s-options-in-a-cmake-project
https://emscripten.org/docs/getting_started/FAQ.html#why-do-i-get-a-nameerror-or-a-problem-occurred-in-evaluating-content-after-a-s-when-i-use-a-s-option

Change-Id: I9cc0a5aece0019c81e3f435106bf288cd68d0fd0

CMakeLists.txt

@@ -631,9 +631,9 @@ if(WEBP_BUILD_WEBP_JS)
     set(WEBP_HAVE_SDL 1)
     set_target_properties(
       webp_js
-      PROPERTIES LINK_FLAGS "-s WASM=0 \
-         -s EXPORTED_FUNCTIONS='[\"_WebpToSDL\"]' -s INVOKE_RUN=0 \
-         -s EXPORTED_RUNTIME_METHODS='[\"cwrap\"]'")
+      PROPERTIES LINK_FLAGS "-sWASM=0 \
+         -sEXPORTED_FUNCTIONS=_WebpToSDL -sINVOKE_RUN=0 \
+         -sEXPORTED_RUNTIME_METHODS=cwrap")
     set_target_properties(webp_js PROPERTIES OUTPUT_NAME webp)
     target_compile_definitions(webp_js PUBLIC EMSCRIPTEN WEBP_HAVE_SDL)
   endif()
@@ -644,9 +644,9 @@ if(WEBP_BUILD_WEBP_JS)
   target_include_directories(webp_wasm PRIVATE ${CMAKE_CURRENT_BINARY_DIR})
   set_target_properties(
     webp_wasm
-    PROPERTIES LINK_FLAGS "-s WASM=1 \
-       -s EXPORTED_FUNCTIONS='[\"_WebpToSDL\"]' -s INVOKE_RUN=0 \
-       -s EXPORTED_RUNTIME_METHODS='[\"cwrap\"]'")
+    PROPERTIES LINK_FLAGS "-sWASM=1 \
+       -sEXPORTED_FUNCTIONS=_WebpToSDL -sINVOKE_RUN=0 \
+       -sEXPORTED_RUNTIME_METHODS=cwrap")
   target_compile_definitions(webp_wasm PUBLIC EMSCRIPTEN WEBP_HAVE_SDL)
 
   target_compile_definitions(webpdspdecode PUBLIC EMSCRIPTEN)

webp_js/README.md

@@ -26,20 +26,21 @@ Emscripten and CMake.
 
 -   compile webp.js using 'emmake make'.
 
--   that's it! Upon completion, you should have the webp.js and webp.wasm files
-    generated.
+-   that's it! Upon completion, you should have the 'webp.js', 'webp.js.mem',
+    'webp_wasm.js' and 'webp_wasm.wasm' files generated.
 
 The callable JavaScript function is WebPToSDL(), which decodes a raw WebP
 bitstream into a canvas. See webp_js/index.html for a simple usage sample (see
 below for instructions).
 
 ## Demo HTML page
 
-The HTML page webp_js/index.html requires an HTTP server to serve the WebP image
-example. It's easy to just use Python for that.
+The HTML page webp_js/index.html requires the built files 'webp.js' and
+'webp.js.mem' to be copied to webp_js/. An HTTP server to serve the WebP image
+example is also needed. With Python, just run:
 
 ```shell
-cd webp_js && python -m SimpleHTTPServer 8080
+cd webp_js && python3 -m http.server 8080
 ```
 
 and then navigate to http://localhost:8080 in your favorite browser.
@@ -48,9 +49,11 @@ and then navigate to http://localhost:8080 in your favorite browser.
 
 CMakeLists.txt is configured to build the WASM version when using the option
 WEBP_BUILD_WEBP_JS=ON. The compilation step will assemble the files
-'webp_wasm.js', 'webp_wasm.wasm' in the webp_js/ directory. See
-webp_js/index_wasm.html for a simple demo page using the WASM version of the
-library.
+'webp_wasm.js' and 'webp_wasm.wasm' that you then need to copy to the
+webp_js/ directory.
+
+See webp_js/index_wasm.html for a simple demo page using the WASM version of
+the library.
 
 You will need a fairly recent version of Emscripten (at least 2.0.18,
 latest-upstream is recommended) and of your WASM-enabled browser to run this