index: consistent naming

index: consistent naming

Replaced use of run_query with each_docid
Rename instances of ferret query objects to 'ferret_query'
Rename 'build_query' to 'build_ferret_query'
Rename hashes passed to index methods to 'query'
Rename 'parse_user_query_string' to 'parse_query'
Change 'parse_query' to return a query hash
Rename 'drop_entry' to 'delete' and modify callers to pass msgid