ENH: Series constructor converts dicts with tuples in keys to MultiIndex
closes #3323
related #4187
related #1848

Hi,

I'd love for Series (and DataFrame) initialized with a dict to automatically create the MultiIndex.  See below example.

Desired Result:

```
In [1]: pandas.Series({('a', 'b'): 1, ('a', 'a'): 0, ('a', 'c'): 2, ('b', 'a'): 3, ('b', 'b'): 4})
Out[1]:
a  a    0
   b    1
   c    2
b  a    3
   b    4
dtype: int64

In [2]:
```

Current result:

```
In [1]: pandas.Series({('a', 'b'): 1, ('a', 'a'): 0, ('a', 'c'): 2, ('b', 'a'): 3, ('b', 'b'): 4})
Out[1]:
(a, a)    0
(a, b)    1
(a, c)    2
(b, a)    3
(b, b)    4
dtype: int64

In [2]:
```

Is this something I can go ahead and update tests for?  It seems like we should have it.  

Also, what are your thoughts about adding this to the DataFrame constructor as well?

Thanks,
Alex
