Modularize emscripten build.

By default, emscripten's generated javascript modules lives in the global object "Module'.

This makes it impossible to load multiple emscripten modules on the same page.

In attempt to avoid namespace collision, this change modularizes the emscripten build so the Module is instead called 'BASIS'.

Many target applications for Basis are likely to already be using other emscripten modules.

Testing:

The existing webgl/(texture|gltf) pages have been updated to use the new name and seem to operate as before

webgl/gltf/index.html

@@ -15,7 +15,7 @@
 
 <body>
   <script>
-    Module.onRuntimeInitialized = () => {
+    BASIS().then(Module => {
 
       const { BasisFile, initializeBasis } = Module;
 
@@ -97,7 +97,7 @@
 
       }, false );
 
-    }
+    });
 
     function log(s) {
 

webgl/texture/index.html

@@ -258,7 +258,7 @@ function viewAlpha() { drawMode = 2; redraw(); }
   <div id='logger'></div>
 </body>
 <script>
-  Module.onRuntimeInitialized = () => {
+  BASIS({onRuntimeInitialized : () => {
     var gl = elem('canvas').getContext('webgl');
     // Load the DXT extension, and verify it exists.
     if (!gl.getExtension('WEBKIT_WEBGL_compressed_texture_s3tc') && !gl.getExtension('WEBGL_compressed_texture_s3tc')) {
@@ -275,6 +275,6 @@ function viewAlpha() { drawMode = 2; redraw(); }
     }, false);
 
     runLoadFile();
-  }
+  }}).then(module => window.Module = module);
 </script>
 </html>

webgl/transcoder/CMakeLists.txt

@@ -17,5 +17,5 @@ if (EMSCRIPTEN)
   set_target_properties(basis_transcoder.js PROPERTIES
       OUTPUT_NAME "basis_transcoder"
       SUFFIX ".js"
-      LINK_FLAGS "--bind -s ALLOW_MEMORY_GROWTH=1 -O3 -s ASSERTIONS=0 -s MALLOC=emmalloc")
+      LINK_FLAGS "--bind -s ALLOW_MEMORY_GROWTH=1 -O3 -s ASSERTIONS=0 -s MALLOC=emmalloc -s MODULARIZE=1 -s EXPORT_NAME=BASIS ")
 endif()