Use array of strings for toml dependencies

[cnpryer]

Closes #188

Summary of changes

- Change order of project table attributes.
- `PythonPackage` is initialized with a string (TODO: name and version parsing).
- Remove dev-dependencies from toml.
- Change dependencies to array of strings in toml.
- Update tests

This introduces a quirk where the dependencies in the toml must be defined before the [[project.authors]]. But the authors is already a quirk. So it's a 2-for-1 for now.