[Parallel] Minor style change
[Parallel] Index: Using accumArray on buildQueryIndex

The accumArray function fills the sections with no entry with default
values while the array function leave the gaps with undefined. When we
need to force the array evaluation with deepseq, if there is any
undefined value on the array an exception will be raised.
[Parallel] Performing queries

Some limitations:
    - Just text passage queries are allowed
    - Just one query per execution
    - Using just one subindex