cheapr 1.0.1

• R version 4.0.0 now required as also required by cpp11.

• New function int_sign for integer-based signs.

• overview now prints slightly differently. Specifically 'class'
  is not printed. Time series overviews now return and print the growth rate.

• cheapr's internal cpp_list_as_df now always returns a data frame with
  names, even when supplied an empty list.