csvpy: Accept python commands on the command line or in a file

[halloleo]

In order to use csvpy in a non-intractive manner it could accept python commands on the command line or in a file. E.g :

csvpy -f file.py data.csv

This would make it possible to do the same csvpy operation on multiple CSV files. Big win!

[jpmckinney]

A related idea. In #610, @fgregg wrote:

one thing i’ve often wished for is passing a little code into csvpy on the command line that could make this really composable

something like csvpy -c identifier -p “d.lower()” example.csv