properties = parser.acceptsAll( asList( "props", "properties" ), "key=value pairs" )
.withRequiredArg().withValuesConvertedBy( new PropertiesConverter() );
propertiesFromFile = parser.accepts( "properties-file", "filename" )
.withRequiredArg().withValuesConvertedBy( new PropertiesFileConverter() );
extensions = parser.acceptsAll( asList( "exts", "extensions" ), "file name extension to associate with format, .csv, .tsv, ..." )
.withRequiredArg().withValuesSeparatedBy( ',' );
//TODO what is this. Invalid as command.properties-file