Timestamp.now() throws an Error
Not sure if that is expected, but if it is expected it would be nice if the error message and the docsring of `Timestamp.now()` could be improved.

```
from pandas.tslib import Timestamp
Timestamp.now()

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-45-634034a47269> in <module>()
----> 1 Timestamp.now()

C:\portabel\Python27\lib\site-packages\pandas\tslib.pyd in pandas.tslib.Timestamp.__new__ (pandas\tslib.c:5167)()

TypeError: __new__() takes at most 5 positional arguments (9 given)
```
