Add Brazilian federal government import scripts (#60)

Creates a `script/migrate` directory as per #60.

Includes a shell script to download & unpack the data for Brazilian federal government, as well as a Python script to convert the xml files to the standard csv. The Python script has a few dependencies which have to be installed before using (see README).

This merge will also move the previously existing `process.py` script (which migrates from the old to the new csv schema) to a new `migrate` directory.