Split the update script into two

This makes testing easier (e.g. I can run get_pypi_status.py on just a
subset of packages).
Ignore test files (*.json)
Script to extract dependency information from sdists
Bugfix: get_deps.py should skip unreleased packages
Trim trailing whitespace from JSON output
Prettier error formatting
New option: get_deps.py --cache-dir (and also --help)