Use multipv search at low depths.
Idea/code partly from jromang and glinscott.

User input for MultiPV is not recognized at these early depths,
which should be no problem for testing.

bench: 9305288
Use multipv search up to depth 10. Take 2.
bench: 10184765
Use MultiPV search at depth 1

Idea/code partly from joster, jromang and glinscott.
Use MultiPV search up to depth 3.

Experimental.