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()