Rename hasNext to hasNextPage and hasPrevious to hasPreviousPage

I noticed a disparity between `getNextPage` and `hasNext` functions. I hope that with this fix, they will look a little more symmetrical.

Still TODO:
- [ ] make sure the tests pass (I couldn't find anything in the README on how to run the tests)
- [ ] update CHANGELOG
- [ ] make minimised version is up to date
- [ ] make sure `api` folder is up to date
- [ ] make sure `test/coverage` is up to date