Feature request: add violin plot as a DataFrame method
Hi pandas developers,

Is it possible to add violin plot as a built-in DataFrame method, along with bar plots, box plots, etc.? To be specific, I would like to have the following effect:

```
df = pd.DataFrame(______some_dataframe_with_four_columns___)
df.violin_plot()
```

And then I will be able to visualize the distributions of each four columns of `df` side by side, with column names being X axis label names.

Currently, Matplotlib supports generating violin plots from a transposed DataFrame, i.e.,
```
plt.violinplot(df.T)
```
but I need to write additional codes to set the X tick labels, therefore it would be great for pandas to add violin plot plotting as a native method.

By the way, although `seaborn` has a violin plot plotting function, that function does more things under the hood, for example, it aggregates all rows in a data frame by the categorical values of a certain column. This philosophy is not the same as pandas' plotting methods.