Allow setting quoting
Allow setting the quoting type for to_csv. Adds "qouting" argument to the to_csv method of DataFrame and pass this on to the csv.writer. Can then use the defaults from the standard library to set the desired  type of quoting, like so:

import csv
...
dataframe.to_csv(filepath, quoting=csv.QUOTE_NONNUMERIC)
...

FYI this commit breaks the test suite. I'm cleaning it up, but keep in mind for the future
 Thanks. Will remember to run the test suite next time.
