Automatically pull credentials from env

[expede]

Problem

Having to pass in the URL and credentials every time, and grabbing the credentials in every module, is unnecessary boilerplate. Especially annoying for Heroku, where these can be assumed to be available.

Solution

Default to standard env vars, via a default argument value or similar. Still allow overwriting the credentials in case someone wants to be explicit.

"INTERPLANETARY_FISSION_URL"
"INTERPLANETARY_FISSION_USERNAME"
"INTERPLANETARY_FISSION_PASSWORD"