BibtexParser will be in "plugins.citationParser"
Bibtex will be in "lib.pkp.plugins.citationParser"
the outher folder contains: version.xml and "PKPBibtexCitationParserPlugin.inc.php" class that imports "lib.pkp.plugins.citationParser.PKPBibtexCitationParserPlugin"
the inner folder; bibtex contains locale and filter folders where the actual parsing is done, like the other parsers.