Bump version to 0.3.1

Bump version to 0.3.0

Bump version to 0.2.0

Performance enhancement for NO_PROXY

We don't need the full Unicode machinery for lowercase conversion,
since valid domains must consist of ASCII characters.

* Replace to_lowercase() with ASCII normalization.

* Use more descriptive variable names.

* A minor doc tweak in anticipation of further work.

Documentation fix