Unify API

[lassevk]

The API is divided into two distinct sections now, the aligned diffs, and the unaligned diffs. These have different method signatures and different result types.

For v2, a complete overhaul of the entire API is planned, unifying the API into one common API that handles both cases, depending on behaviors or parameterization to signal whether an aligned diff is requested or not.

[lassevk]

New API almost done, will separate the old unaligned diff and the old aligned diff with two new types, diff sections and diff elements. The basic diff output is sections, specifying sections of elements from the two collections that were matched or unable to be matched. These sections may contain numerous elements on both sides.

Sections can be fed to an alignment implementation that will attempt, for each section, to align elements within. The result is a sequence of diff elements, where each such element can hold at most one element from each collection, but can also specify "holes" in terms of missing elements. As an example, an element that only occurs in the second collection is considered to be an inserted element, and will be "aligned" with a missing element form the first collection in the right place in the sequence.