Make "setup.py test" work

Also use it in tox so the integration is tested along the rest.
Some minor style issues
Initial work
Fix docstring
Clarify that immutability isn't recursive
Optimize some

- try side-step immutable's sentry in with_init
- don't create a new sentry for each instance
Reflow docstring
Merge pull request #15 from hynek/immutable

Add @immutable

Fixes #14
Be mutable by default
Add keyword-aliasing for underscores
Add aliasing examples
Fix doctests
Tweak docs
Merge pull request #13 from hynek/private-attrs

Add keyword-aliasing for underscores

Fixes #6.
Tweak changelog
Raise AttributeError on immutability violations
Initial work
Add changelog entry
Join ifs
Add an example