Python dependencies

Example API calls: https://pydeps.herokuapp.com/requests, https://pydeps.herokuapp.com/requests/2.21.0. This pulls all top-level dependencies for the requests package, and the dependencies for version 2.21.0 respectively. There is also a POST API for pulling info on specified versions. The first time this command is run for a package/version combo, it may be slow. Subsequent calls, by anyone, should be fast. This is due to having to download and install each package on the server to properly determine dependencies, due to unreliable information on the pypi warehouse.