Improved flatten

Now it properly handles non-iterable objects.
Thanks goes to @hmax for PR #10

Fix bug in Maybe

That was introduced in 1.2.6

Persistent Maybe

Now Maybe reverts to the initial state, not to disabled state.

Use more new-style classes

In Modifier and Construct tree.

Fix reused and uplink interaction

Thanks goes to @hmax for filing the #8.

Uplinks now misbehave a bit less. Declared behaviour has not changed.

New fancy "Another" modifier

Thanks goes to @true3HAK for PR #7

1.2.2 re-release

Fixed pypi pwd to properly release via travis.

Fix misbehaving collections

Fixed #3 via #6

May cause a couple of backward compatibility issues, but it actually makes this thing work as intended.