Support .broadPeak files

Added support for .broadPeak files. Can use read_bed(…) because
.broadPeak has the same first three columns as .bed which are the only
ones used by ChIP-Enrich anyway.
Added support for .narrowPeak files

In order to use output from MACS2 we need to support .narrowPeak files
which are essentially the same as .bed files, but with more
information. The first three columns are the same.
Merge branch 'develop1'
Merge branch 'develop2'