ENH: Use multiindex levels for function arguments in apply
Currently it is easy to apply functions to the data in a row or column using apply.  However, when important parameters for the analysis is contained in the multiindex for the row or column being analyzed (that is, the column index when analyzing along a column or the row index when analyzing along a row), there is currently no easy way to make use of these parameters.  

I think it would be useful if users could provide a dictionary that maps index levels to function arguments to use when applying a function to a pandas Series, DataFrame, Panel, or Grouper.

Some specific examples:
1. One of the multiindex levels is sampling frequency, which varies across rows.  You want to do the fft of each row, but you need the sampling frequency for that.
2. One of the multiindex levels is the total duration of each recording, and you want to do a count of events per unit of time.
3. Each element is a time point.  One of the multiindex levels is the minimum allow of the recording and another is the stop time, and you want to slice the results to only include values between the start and stop.

These are all easy if the values are the same for all rows or columns, but become much harder currently if they vary.
