Parse a (string) loci expression and add it to the builder.
Parse a (string) loci expression and add it to the builder. Example expressions:
"all": all sites on all contigs.
"none": no loci, used as a default in some places.
"chr1,chr3": all sites on contigs chr1 and chr3.
"chr1:10000-20000,chr2": sites x where 10000 <= x < 20000 on chr1, all sites on chr2.
"chr1:10000": just chr1, position 10000; equivalent to "chr1:10000-10001".
"chr1:10000-": chr1, from position 10000 to the end of chr1.