First steps towards appcepting a range of datasets. The following
functions work fine already but it nees some refactoring to clean
the code.

bef.getDataset(dataset_id=c(7,6), user_credentials="UtsgGiBnEpkCcErn6ZZ7")
bef.getdata(dataset_id=c(7,6), user_credentials="UtsgGiBnEpkCcErn6ZZ7")

This is discussed in #4