Add currrying decorator.

[aitjcize]

Add curried decorator, the function is called as soon as the arguments are all given:

>>> from fn.func import curried
>>> @curried
... def sum5(a, b, c, d, e):
...     return a + b + c + d + e
...
>>> sum5(1)(2)(3)(4)(5)
15
>>> sum5(1, 2, 3)(4, 5)
15

[kachayev]

Cool! I'll update your code with decorator wrapper to deal with origin docs etc.