zpm prototype

This implements the basic functionality for zpm, which includes:

* creating new empty projects
* bundling existing projects into `.zar` files

TODO:

* write tests (and refactor functions to make things easier to test)
* revise the command line interface such that we can run `zpm new` instead of `zpm --new`, etc.
* document use cases and contents of project `.ini` files (`zar.ini`, `meta.ini`, etc.)