hgcli: add stub PyOxidizer project Using commit c772a1379c3026314eda1c8ea244b86c0658951d of PyOxidizer, I ran `pyoxidizer init-rust-project hgcli` to create a stub Rust project. The only modifications I made from what that command produced are: * Update location of pyembed crate to PyOxidizer's Git repository. * Removed some trailing whitespace from pyoxidizer.bzl * Added auto-generated Cargo.lock file Subsequent commits will modify the stub project to Mercurial's needs. Differential Revision: https://phab.mercurial-scm.org/D8350