Rename files

22. Rename the function’s source and test files by calling rename_files("old_name", "new_name")

rename_files("strsplit1", "str_split_one")
# ✔ Moving 'R/strsplit1.R' to 'R/str_split_one.R'
# ✔ Moving 'tests/testthat/test-strsplit1.R' to 'tests/testthat/test-str_split_one.R'