Improve compatibility with Shredder Classic GUI

This commit fixes two issues:

1) Don't print PVs after the search has been interrupted

    This solves the "mate 0 upperbound" scores that sometimes
    creep up when a multi-PV analysis gets interrupted with
    the `stop` command.

2) Print multipv before score

    Shredder Classic fails to identify the main PV
    (the one with multipv 1) if `score` comes first.
    This leads to an eval graph that doesn't reflect
    the scores actually reported by Stockfish when
    doing a multiPV analysis.

No functional change

Closes #76
Tune PawnsFileSpan

Passed the following SPRT tests:

STC:
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 24428 W: 5056 L: 4880 D: 14492

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 26590 W: 4715 L: 4472 D: 17403

Bench: 6615949

Resolves #78
Speed up max_piece_type()

Write code in the way that allows compiler to perform loop unrolling.

My measurement (32 cycles each):

Orig:

Time (Mean: 2466.59375, Trimmed mean: 2464.25, Std: 12.6869487803348)
Nodes (Mean: 4294458, Trimmed mean: 4294458, Std: 0)
Speed (Mean: 1741.09247987678, Trimmed mean: 1742.72879715475, Std: 8.93612608292678)

Time (Mean: 2470.15625, Trimmed mean: 2468.75, Std: 12.7484581610433)
Nodes (Mean: 4294458, Trimmed mean: 4294458, Std: 0)
Speed (Mean: 1738.58176151341, Trimmed mean: 1739.54618465403, Std: 8.95585822316946)

Mod:

Time (Mean: 2449.90625, Trimmed mean: 2445.9375, Std: 12.1000116635508)
Nodes (Mean: 4294458, Trimmed mean: 4294458, Std: 0)
Speed (Mean: 1752.94829372932, Trimmed mean: 1755.75934908231, Std: 8.61478453124504)

Time (Mean: 2442.78125, Trimmed mean: 2441.1875, Std: 8.17839157228837)
Nodes (Mean: 4294458, Trimmed mean: 4294458, Std: 0)
Speed (Mean: 1758.03872783803, Trimmed mean: 1759.16825356261, Std: 5.81131316346191)

No functional change
A small clean up of previous patch suggested by Marco

No functional change