DOC: DataFrame() not included in API reference
The docstring of `DataFrame()` is not present in the documentation (so no 'generated/pandas.DataFrame.html'), because it is not included in the API reference (http://pandas.pydata.org/pandas-docs/dev/api.html).

But there is one for `DataFrame.__init__()` (http://pandas.pydata.org/pandas-docs/dev/generated/pandas.DataFrame.__init__.html#pandas.DataFrame.__init__), which seems not that usefull.  
Do I replace the init version with DataFrame itself, or should I just add a line for DataFrame in api.rst?

The same applies for Series and Panel.
