[cudamapper] compared to minimap2

[wzboy1984]

Hi,

I've tried doing alignment by cudamapper over 3 datasets, and compared to that by minimap2.
The time costs don't reduce much when compared to minimap2. In some cases, the running speeds of cudamapper are slower than minimap2, as shown in the below table.

	Name	wall time(s)	mem peak(G)	note
data 1	cudamapper	650.63	10.87	v100, 16G
	minimap2_v2.20	1687.86	31.53	-t 32 -k 17 -w 17 -x ava-ont
data 2	cudamapper	11193	39.76	v100, 16G
	minimap2_v2.20	4491	19.21	-t 32 -k 17 -w 17 -x ava-ont
data 3	cudamapper	5958	27.4	NVIDIA TITAN xp, 12G
	minimap2_v2.20	4590	54.02	-t 32 -x ava-ont

Also, the sensitivity of the cudamapper alignments is lower than that of minimap2, which leads to the poorer assembly results based on cudamapper alignments of the 3 above datasets. The algorithm of cudamapper might need to be modified to get alignment results similar to minimap2.