ENH: add option chop_threshold to control display of small numerical values as zero
Doesn't cover complex numbers for now (no formatter implemented in format.py)

I think the "supress" kwd choice in numpy is not that awesome. So I borrowed `chop` from 
the mathematica parlance.
#2734

It does what I asked - Thanks!

There is one improvement I think we could make. Assuming I have set the `precision` option to 5, when displaying a chopped entry near other data in scientific format (something like `2.54443e-03`), the chopped value will display as`0.00000e+00`. It would be nice if it just printed `0` instead of `'0.' + '0' * precision + 'e+00'`.

A side note, is there a way to control if things are printed in scientific format (with the e's)?
 You can look at the code for `pandas.set_eng_float_format` to see how it's done,
and you can pass your own formatters to `to_string()` for even more control.
 cherry picked. thanks
 added mention to v0.11.0.txt and pushed.
