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