Make merge-reduce unit tests work

[spacekookie]

That can be done in two ways (one simple, one not so simple)

1. Making some assumptions and counting state, analysing the clause often before making a move
2. Implement a trial system and backtracking in case a branch didn't work out

Regardless of what is chosen, there are some things that need to be implemented nonetheless

• Instead of calling reduce there needs to be a consider_reduce_choices function which returns a set of terms that can be acted on, saying what operation can be performed
• The reduce function then needs to build priorities according to the resolution rules
• Record every action taken in the clause history (implement a queue?)
• Add a results struct into the clause that can be slowly filled with data as it trickles in

Derivations are simple and can immediately lead to a field in the result struct.

Merges are a bit more complicated because they might need to be performed in a specific order { A, B }, { !A, D }, { A, B! } for example.

To be continued