[Retros] more 8th rank pawn mates

[andrew buchanan]

Cases that hadn't been handled before:

dxeR
rnb1kbnr/pp1ppppp/8/q1P5/8/4P3/PP2BPPP/RNB1rKNR
PG in 6.0
(sim for dxeQ)

fxeR
rnk1Rbnr/ppp1p1pp/3p4/8/B3b3/8/PPPP1PPP/RNBQK1NR
PG in 6.5

(So we have an answer now for each of the R&Q cases.)

Improved ones:

gxhR
rnbqk2R/pppppp1p/6p1/7R/3n4/8/PPPPPPP1/RNBQKBN1
PG in 5.5
(sim for gxhQ)

hxgR
rnbqk1R1/pppppp2/4rbp1/8/8/3P4/PPP1PPP1/RN1QKBNR
PG in 6.5
(sim for hxgQ)

cQ
rnQ1kbnr/pp2pppp/2b5/3p4/8/8/PP1PPPPP/RNBQKBNR
PG in 4.5

fQ
rnbqkbnr/pppppp1p/8/8/4B1Q1/4P3/PPPP2PP/RNBK1qNR
PG in 5.0

Cheers,
Andrew.