Accessor for axioms/definitions

[anyhannah]

Two functions added:

1. Look up definitions of an ont type; e.g. ont['asleep-val'].definitions
2. find ont types whose definitions have the given ont type; e.g. ont['d::move']

• Returned definitions are lists of strings in uppercase, just as in the ontology.json file. For example, ont['asleep-val].definitions returns ['NOT', ['AWAKE-VAL', 'FIGURE', '?NEUTRAL']]

[anyhannah]

Correction: Returned definitions are (nested) lists of strings.