Replace `std::env::home_dir()` with `home` crate impl.

* Import the `home` crate in `util/dir`.

* Replace uses of `env::home_dir()` with `home::home_dir()`.
  * `home` uses a 'correct' impl. on windows and the stdlib impl.
    of `::home_dir` otherwise.

* Reexport `home::home_dir` from `util/dir`.

* Bump `util/dir` to 0.1.2.