API reference is missing the Plotting module
I noticed this when looking for the documentation page for the `scatter_matrix` function.

#### Problem description

I needed to check the parameters I needed to pass to `plotting.scatter_matrix`. Had to go all the way to the source code.

Turns out none of the functions in `_misc.py` are included in the API reference. I added a **Plotting** section after **General functions** and before **Series**. Under that section I added a **Miscellaneous** section which includes:

- scatter_matrix
- radviz
- andrews_curves
- bootstrap_plot
- parallel_coordinates
- lag_plot
