code: def get_files():
      
      sources = []
      headers = ["datatable/include/datatable.h"]
      assert os.path.isfile(headers[0])
      for dirpath, _, filenames in os.walk("c"):
          for f in filenames:
              fullname = os.path.join(dirpath, f)
              if f.endswith(".h") or f.endswith(".inc"):
                  headers.append(fullname)
              elif f.endswith(".c") or f.endswith(".cc"):
                  sources.append(fullname)
      return (sources, headers)
docs: Return the list of all source/header files in `c/` directory.
  
      The files will have pathnames relative to the current folder, for example
      "c/csv/reader_utils.cc".