Ability to configure devDir with flag [#21]

Potential fix for issue #21 that adds ability to use a flag called `--dev-dir`, and a check for `XDG_CACHE_DIR` before `HOME`.

The `--dev-dir` flag is the be-all-end-all result. If this flag is not used, then the application looks for `XDG_CACHE_DIR` first, then `HOME`, then `USERPROFILE` as it used to.