Add cpal recipe

recipes/cpal/recipe.sh

+GIT=https://gitlab.redox-os.org/redox-os/cpal.git
+GIT_UPSTREAM=https://github.com/tomaka/cpal.git
+BRANCH=redox
+CARGOFLAGS="--example beep"
+
+function recipe_stage {
+    dest="$(realpath $1)"
+    mkdir -pv "$dest/bin"
+    cp -v "target/${TARGET}/release/examples/beep" "$dest/bin/cpal"
+    skip=1
+}