CLN: change print to print() in docs
closes #4967

`print` statements refactoring

@cpcloud can you build these docs just to check?
 @alefnula fyi....in fut make the top of the PR like I did here; then when merged willl auto close the issue
and make the title reflect the issue for easy viewing

thanks! these r gr8
 @jreback sure thing
 hm `numpydoc` not compatible with py3 :(
 at least the version we're using isn't
 @cpcloud But this is also valid py2 code :-/
 yep those are building
 @jreback there's that `to_datetime` failure (@alefnula, unrelated to ur changes) but otherwise things are :ok_hand: in py2 land
 right, I think dan birken still fixing that up
