gmt a cov add-readcounts - simplify header regex
gmt a cov bam-readcount - use same header regex as AddReadcounts
gmt a cov bam-readcount - only check for header on first line
gmt a cov add- & bam-readcount: fix header regexes
Merge pull request #42 from mark-burnett/fix-bam-readcount-header-skipping

Skip possible header lines less aggressively in G:M:T:A:Coverage:BamReadcount