API Additions
- `rouver.args`: Add `parse_args()`, `Multiplicity`, `FileArgument`,
and `CGIFileArgument`.
- `rouver.exceptions`: Add `ArgumentsError`.
- `rouver.html`: Add `http_status_page()` and `see_other_page()`.
- `rouver.status`: Add `status_line()`.
- `rouver.response`: Add `respond_with_html()` and `see_other()`.
- `rouver.router`: Add `Router`.
- `rouver.types`: Add `EnvironmentType`, `HeaderType`,
`StartResponseReturnType`, `StartResponseType`, `RouterHandler`,
`RouterType`, and `RouteTemplateHandler`.