Create @mediabunny/mp3-encoder, restructure and extend build system

packages/mp3-encoder/README.md

@@ -0,0 +1,32 @@
+Build
+
+Compiling LAME:
+```
+emconfigure ./configure \
+    CFLAGS="-DNDEBUG -DNO_STDIO -O3 -msimd128" \
+    --disable-dependency-tracking \
+    --disable-shared \
+    --disable-gtktest \
+    --disable-analyzer-hooks \
+    --disable-decoder \
+    --disable-frontend
+
+emmake make clean
+emmake make
+```
+
+Then extract the file `libmp3lame/.libs/libmp3lame.a`, which you'll need to build the LAME bridge.
+
+Compiling the LAME bridge:
+```
+emcc src/lame-bridge.c build/libmp3lame.a \
+    -s MODULARIZE=1 \
+    -s EXPORT_ES6=1 \
+    -s SINGLE_FILE=1 \
+    -s ENVIRONMENT=web,worker \
+    -s EXPORTED_RUNTIME_METHODS=cwrap,HEAPU8 \
+    -s EXPORTED_FUNCTIONS=_malloc,_free \
+    -msimd128 \
+    -O3 \
+    -o build/lame.js
+```