Refactored find, to_s, and initialize

find:       returns a Dinodex object, where the new Dinodex.entries includes
            the dinosaurs matching the search
to_s:       prints all dinos in the dinodex by default, or prints the dinosaur
            matching the name passed in as the optional arg
initialize: initializes from an (array) of csv filepaths, or initializes an
            empty dinodex
Refactored find some more, added add method

add method allows user to manually add a single (or multiple) dinosaurs
to a dinodex
Redid handling of invalid CSV format errors

Error now raised by Formatter class as InvalidFormatError

Then rescued in Dinodex class, which continues execution -- the
idea being that Dinodex will successfully parse as many input CSV
files as it can, and ignore those that it can't