Vocabulary ID prefix search by specific ontology

vocabulary services support calls for prefix matching for autocomplete, as in http://alpha.neuinfo.org/services/v1/vocabulary?prefix=cranio. However, these calls return all matches for a given prefix or category. Restricting queries to specific ontologies - will be useful for the UI.

For example, we might say
http://alpha.neuinfo.org/services/v1/vocabulary?prefix=cranio&ont=uberon

to find all Uberon terms that start with "cranio"