Added panaroo_2_pagoo function to read the output of the panaroo pangenome reconstruction software.
Improved $add_metadata() method. Now columns with the same name as the one already present are overwritten instead of duplicated (closes #44). Also, users can now provide metadata covering the pangenome partially, i.e, not providing all the gene/clusters/organisms in the mapping column. Those entities without metadata provided are filled with NAs.
NEWS.mdfile to track changes to the package.