Add "Total Edge Cost" calculation

[recursion-ninja]

Use the "single assignment field" to calculate a sanity cost colloquially called "stupid tree cost."

We'll use this value to check the correctness of our algorithms.

Let's call this "Total Edge Cost."

[recursion-ninja]

It's currently over estimating the cost compared to the tree cost.

[recursion-ninja]

After revising the Final assignment states to use a more Sankoff-like derangement approach, the Total Edge Cost matches the Tree Cost after some initial testing. To make this efficient, the memoized TCM will need to be expanded to accept 3 character states. See #33.