Add recipe for RustPython

recipes/rustpython/recipe.sh

+GIT=https://github.com/RustPython/RustPython
+BRANCH=redox-release
+CARGOFLAGS=--no-default-features
+export BUILDTIME_RUSTPYTHONPATH=/lib/rustpython/
+
+function recipe_stage() {
+  dest="$(realpath "$1")"
+  mkdir -pv "$dest/lib/"
+  cp -r Lib "$dest/lib/rustpython"
+}