Refactored read method

read_csv renamed to read_file_and_format, since it not only reads
the CSV file, but also returns the format (in the form of a Formatter
object)

read_csv also now rescues Errno::ENOENT (file not found); in case of
file not found, skips that file and continues execution, for same reasoning
that we rescue InvalidFormatError

speaking of, change read_file_and_format to rescue InvalidFormatError
rather than general RuntimeErrors ...