Add ability to modify or friendly format numerical values

[victorhooi]

It would be useful to have an option that friendly formatted or applied modifiers to numbers.

For example, if you had the float:

5081998.9369165478

It would print it out as:

5,081,998.9369165478

I'm currently printing out a large table of numbers using csvlook, and it would be much more readable if I could add commas to all the numbers, so I can get a rough idea of scale (particularly since the numbers are all left-aligned, and not right-aligned, and I can't seem to find a way in csvkit to change that).

Or you might have modifiers to truncate the fractional part, rounded up/down etc. which you can apply before printing.

[jpmckinney]

The implementation of this functionality is moving out of the csvkit repository into its new dependency agate (#515). This is the file that would need to be modified. You may re-open your issue on agate.