Mission to free Bool_ from Either

- So far done with the Maple, Sample and Expect interpretations
Disintegrate grants some freedoms to Bool_

- WARNING: it typechecks, but is incomplete
- Only true and false are implemented
  - Unsure if done correctly!
  - Ord' and Show' instances for Tree are incomplete
- if_ has not been implemented yet
Partial, PrettyPrint, and TH also free Bool_ from Either