Feature requests: pandas.DataFrame.quantile with exclusive/inclusive of median
There seems to always be the debate when calculating the 1st and 3rd quartiles in statistics about whether the median is included or not included in calculating the q1, q3. Some calculations include the median, while other exclude it. Regardless of the "correct" way to calculate this out, it would be nice if pandas could accommodate both scenarios, with a parameter of some sort, maybe `include_median = False` to get the results.

For example:

Looking at this series of values:

```
s = pd.Series([.0022, .0032, .0043, .0043, .0059])
s.quantile([0.25,0.5,0.75])
```

yields a result of:

```
Out[41]: 
0.25    0.0032
0.50    0.0043
0.75    0.0043
dtype: float64
```

Which is the median of the lower and upper halves (including the median value)
When I am looking for the results of, something along the lines of:

`s.quantile([0.25,0.5,0.75], include_median = False)`

```
0.25    0.0027
0.50    0.0043
0.75    0.0051
dtype: float64
```

which would be the medians of the lower and upper halves (excluding the median value from those sets)
