Pass through the kwargs to the various interpolators
Many of the interpolators have additional arguments so why not pass the `kwargs` collected by [`interpolate`](http://pandas.pydata.org/pandas-docs/dev/generated/pandas.Series.interpolate.html) function to the underlying interpolators?

For example the [spline](https://github.com/pydata/pandas/blob/821542fb1dfd55b0e0d25e55eb4fee6555d01cbd/pandas/core/common.py#L1737) function can also take a smoothing factor `s`.
