Consolidating multiple issues here:

• blacklist BED file with one entry csv sniffer fails, when given only a single line of BED-like input #196
• bg2 file with a header TSV importer that supports headers #128
• malformed pairs file Add input validation for out of bounds column numbers #135
• spaces instead of tabs in chromsizes file add input validation for util.read_chromsizes  #124
• other chromsizes weirdness cryptic error message when chromsizes is not formatted properly #142