some compare result of minimap2 '-x sr' mode of v2.18 and v2.20

genome: GRCh38.p13
data: Illumina PE150

a) performance: big change in runtime.
v2.18
real 213.72(3:33.72), user 12295.66, sys 169.28
v2.20
real 323.90(5:23.90), user 17924.58, sys 225.08
but memory usage is almost same.

b) mapping result: big change in 'properly paired %' and 'singletons %'

v2.18
mapped % 97.16%
mapq>=1 % 92.69%
properly paired % 95.98%
singletons % 0.30%
v2.20
mapped % 96.34%
mapq>=1 % 92.01%
properly paired % 92.63%
singletons % 1.07%

c) misc
in man file, '-r50' is in '-x sr' mode,
but '-r100' is in source(mo->bw = mo->bw_long = 100;).