blacklisting region from a region file

[chklopp]

I would like draw the assembly graph after having removed the alternative haplotype (extracted using purge_dups) from an assembly graph gfa file. Could you add a feature to gfatools blacklist to produce a new gfa from an input gfa and a list of regions to remove?
The region could be given as a simple one column file, with one region per line, or comma separated in a command line option.