Moves tests out of the package.
Tests that proxied objects are not affected when the proxy is wrapped by unboxed.

`unboxed` has the wrong name: it should be called to something that reminds
that the proxy object won't proxy. Alternatives: unproxify, dontproxy
Fixes bug: when the proxy class does not have a behaves attribute, it should not raise an exception
Renames `target` to `proxy` in the context of the `unboxed`(unproxify).

Actually the argument to `unboxed` it's assumed to be a proxy class, or
at least a class that behaves differently under UNPROXIFING_CONTEXT.
Uses a lambda instead of a partial, so that we can pass the docs to weaved method. xoutil.aop.classical.
Uses pytest instead of nose to discover and run tests
Marks next release as 1.2.3
Minor doc fixes
Corrects some typos
Begins history for 1.2.3
Marks (temporarily) the next release as 1.2.4