ENH: support str translate for StringMethods
as a part of https://github.com/pydata/pandas/issues/9111

note that this handles both py2 and py3 as the signature for `str.translate` has changed from py2 to py3 

@sinhrks @jreback  

I don't know if I find it a good idea to have different behaviour for python 2 vs 3. Why not just going with the python 3 signature?
 the thing is it's more than the signature that changed from python 2 to 3. The meaning of `table` in `str.translate` also changed. If we only have the python 3 signature, users of python 2 would lose functionality with this method. In particular, users of python 2 would not be able to delete characters with `StringMethods.translate`, because there's no way to specify that in the python 2 structure of `table`.
 Correct, but I think single internal func is better for API doc on the website to show both python 2 and 3 info. How about:
- Merge to single function to accept both `table` and `deletechar`.
- Ignore `deletechar` in python 3 with warning, and describe it in docstring.
 If the change between python 2 and 3 is that big, I think even more reason for us to choose one behaviour (and thus, python 3 behaviour is of course the most logical). Users of python 2 will eventually have to change their code for python 3, so if they start using the pandas string method, they can already adapt (and otherwise they can always use the apply approach). We should follow the behaviour of the standard string methods as much as possible, but here I would personally deviate.
I would just put a warning in the docstring that it follows python 3 behaviour.

Do you know if there is a reason the behaviour changed? Did the functionality goes elwewhere?
 so first of all, don't get me wrong - I think the python 3 signature is better and I'm a big advocate for using python 3. It's just that sticking with the python 3 signature in our implementation means that python 2 users will lose some functionality. And I'm open to making that tradeoff.

@jorisvandenbossche just to be clear, no functionality of the standard `str.translate()` has gone somewhere else from python 2 to python 3. The `deletechars` kwarg gets dropped in python 3 because the python 3 `table` format is flexible enough to let users specify deletions. 
 so, python 2 users won't really lose some functionality, but just have to adapt their code somewhat?

I also understand the reasons to go for python 2/3 dependent behaviour, but as this is a 'new' feature for pandas, I would lean towards making a choice for 'one way', as we have the choice to do that 
 @jreback @shoyer some opinion?
 @jorisvandenbossche if we make the signature `StringMethods.translate(table)` for both python 2 and python 3, then users of python 2 _will_ lose the ability to pass `deletechars`. Users of python 2 can't specify deletions in the python 2 `table` format.
 Ah, sorry, I didn't really look in detail to the `str.translate` method. I thought the `table` was just a normal argument, instead of a special string you can generate with a function. OK, no problem then!
 I think the suggestion of @sinhrks is good then, having one docstring that has information for both python 2 and 3 (as we don't have separate docs)
 I haven't used `str.translate` before, so I don't have a strong opinion here. I think we agree that we want to be forwards compatible with Python 3 as much as possible while retaining functionality. In this case, it seems like have two function signatures is a pretty reasonable solution -- there's not too much in the way of duplicated code and it is relatively straightforward to document. But @sinhrks's solution would also be fine by me.
 I agree here @sinhrks seems reasonable.
 Sounds good thank you all for the feedback! Will update shortly. 
 updated, please take a look 
 Can you update the docstring here as well?
 @jorisvandenbossche do you mean the release note? 
 yes, of course .. :-)
 yes definitely :) the only thing is that this would be on the same line as the PR for `index(), rindex()`, but I'll update here anyway 
 @mortada this was passing before yes? and you just changed docs right?
 yes this was passing before
 @mortada ok, this needs a rebase now that I merged the other. pls ping when ready.
 ok cool i'll rebase
 ok rebase is done, updated 
 @mortada ok thank you!
 sure thanks a lot! 
