remove julian dates
add cleaned? cleaned! for tracking whether or not a Quandl::Data instance has already been cleaned.
#clean will short circuit if the data is already cleaned
add #row to Operations.
Operations will be passed data_array rather than to_jd.to_a

clone will include cleaned: cleaned as a paramter, so that we avoid cleaning data multiple times
string_to_csv will not force values to float. Allow babelfish to handle this.
Format#parse will force values to float. Used by Quandl::Cassandra::Data since it is a lot faster than babelfish, and we trust C* data