API: default export for to_clipboard is now csv/tsv suitable for excel (GH3368)
closes #3368

We should have a setting `io.clipboard.sep` . Can we change to `\t` for windows/osx by default and I guess `','` for Linux? (set the defaults in config_init, right?)
 `to_clipboard()`'s current behaviour is useful for other things, how about `df.to_clipboard(excel=False)`?
 @jreback `excel=False` is fine, but that'd just be a synonym for `sep=','` right?
 I think we make \t the default, maybe make it a config option as well? `io.clip.sep`?
 @y-p I will update docs/announcemnt not sure an explicity excel kw is necessary
 `df.to_clip()` can be used to paste a nicely-formatted textual table into a document, that's useful as well.
Not sure making an arg for method invocation into a config option makes sense.
 @y-p I actually need to use a sep of ',' to paste as I copy from a linux X window to excel; prob not typical
 there is no easy way to actually form the object prior to writing to the clipboad; eg. we are using to_csv and not to_string.
 right. I thought it'd be best if `to_clip(excel=False)` kept the current behaviour, and `to_clip(1)`
generated a csv. 
 @jtratner @y-p further comments?  do we need an `excel` kw?
 What a bummer to be ignored like that. _sadness_.
 @y-p what do you mean? I never saw a comment when I posted a request for further comments...
 Isn't it clearly better to extend the existing functionality rather then replace it? I made 
that point 3 times early on.
It's totally fine you don't agree, but, what's the reasoning?
 this doesn't actually change much, except for replacing space separation with tabs sep, which _appears_ to be more compatible with various systems. I believe you pointed out the issue, which tab sep fixes, or is this not the case?
 tabs allow you to paste into excel, yeah, but now you can't get an aligned textual table into the clipboard.
`sep=' '` doesn't replicate the old behavior, try it. 
 and how would you propose for an API to handle both of these somewhat discordant cases?

as IMHO I would think pasting to excel is much more important
 What's wrong with what I suggested above?:

``` python
def to_clipboard(excel=False):
    if not excel:
       to_string() # -> clip, original behavior
    else:
       to_csv(sep='\t') # -> clip , new behavior

```

Also, why decide which is more important when it's so easy to allow both while
avoiding breakage to existing behaviour at the same time?
 ok....that's reasonable....guess I misunderstood what you meant....would have have a problem with default `excel=True`? it breaks compat, but I think is more intuitive
 I guess there's not much harm in changing the default,since it's easy
to request the old behavior. It's for interactive use only anyway. so yeah, should be fine.
 +1 on excel=True as the default, if for no other reason that it'd be a
whizbang feature to show off.  Also, I've spent most of the day
copy/pasting into Excel so that's something.
 lol!
 Thanks jeff, it's _just right_ now. :)
 :)
