Add support for tidy select helpers

`sc_select()` currently supports these tidy select helpers:

- `starts_with()`
- `ends_with()`
- `contains()` 
- `matches()`
- `everything()`

Need to add support for:

- [ ] `num_range()` (this may not be useful)
- [ ] `all_of()`
- [ ] `any_of()`
- [ ] `last_col()`