This PR allows the Brute filter parameters to be configured rather than
using fixed constants. It also tweaks the presets to take advantage of
these new options:
o3: level=1, lines=3 (fractionally worse/faster)
o4: level=1, lines=4 (same as before)
o5: level=4, lines=4 (fractionally better/slower)
o6: level=5, lines=8 (slightly better/slower)
The parameters can be explicitly set in both the API and the CLI.
aebddf443a