envreport: why doesn't it work anymore??

Prepare reports on environments and report the differences between two environments.

First and foremost, envreport produces a report on an environment in a diffable format.

Inspired by pyenvdiff, which appears to have gone unmaintained.

Goals

The main goal is to help folks answer the question "It worked here, it didn't work there. WHY? WHAT'S DIFFERENT?!"

Design goals:

1. collect information about an environment, so that it can be easily compared with another
2. be compatible, easily distributable (a single Python script, require only standard library for relatively old Python)
3. be modular, so additional sources of information can be added, as needed
4. always produce something, even if data collection fails