add ListT monad transformer and relevant instances

[chessai]

Relevant issue: #54

Don't merge yet, some unresolved questions:

1. Should we include the Enumerator part of the ListT API from pipes? I have not done so here.
2. Should we incur a dependency on exceptions to provide MonadCatch and MonadThrow instances for ListT? There seems to already be the desire to incur this dependency on exceptions in issue [Discussion] Should we bring back exceptions instances? #52.
3. Should the name of this be ListT, or should it be something else?

[treeowl]

This is very hard to review because it has a slew of formatting changes along with substantive ones. Please separate those out into another commit. One or two are fine, but when there's a huge bunch it makes things really hard.

[chessai]

Understandable; sorry about that. Give me a moment.

[chessai]

see #71