chore: add data CSVs to package_data

[danielolsen]

Purpose

Copy data CSVs when package is installed via setup.py. This will allow the files to be accessed automatically, no matter how the package is installed, via code like:

import inspect
import os
import postreise
postreise_data = os.path.join(os.path.dirname(inspect.getfile(postreise)), "data")

Time estimate

2 minutes.

[BainanXia]

Cool.