And demonstrates usage with the tidyr gather/spread animators. In essence, user-facing functions take an argument `anim_opts = anim_options()` as a last argument (after ... if applicable). These options should be passed through to lower level functions and should be given to `animate_plot()` and `static_plot()`.

This implementation actually doesn't break previous functions, but the join and set families will need to be updated to match.

Adds a few additional dplyr functions to the package imports, in particular: slice, data_frame, and row_number.

- Import packages from tidyverse
- Set global imports in zzzz-package.R
- Import pipe and tidyeval
- Update authors
- Downgrade version to 0.0.1.9000
- Change license to MIT
- TODO: Internal package qualifications still needed, e.g. dplyr::row_numbers()

-id1, -id2 work, id1:id2 does not (yet)