Add a method for plotting a range on a SkewT

[dopplershift]

Description Of Changes

This adds a plot_vertical_range method to SkewT to allow plotting up an indicator of a vertical range of interest, similar to those done in NSHARP/SHARPpy:

The code to add to our Advanced_example.py for that image are:

skew.plot_vertical_range(lcl_pressure, lfc_pressure, 0.25)
skew.ax.text(0.25, lfc_pressure - 20 * units.hPa, 'CIN 250 J/kg', ha='center',
             fontdict={'size': 'large'}, transform=skew.ax.get_yaxis_transform())

skew.plot_vertical_range(105, 260, 0.4, width=0.06, colors=['tab:red'], linewidths=[3, 1.5, 1.5])
skew.ax.text(0.42, 180, 'No Data', color='tab:red', fontdict={'size': 'large'},
             transform=skew.ax.get_yaxis_transform())

As you can see, the labels right now are added by hand. So the todo's and questions to be answered are:

• naming? I'm not sure how I feel about plot_vertical_range(). draw_vertical_range()? Is a "vertical range" even the right terminology?
• Is it worth adding labelling? To what extent? Depending on how much control we add, it could really bloat the API.
• add tests
• Include in example(s) (?)

Checklist

• Tests added
• Fully documented

[ejt4m8]

Perhaps a more appropriate name would be draw_vertical_depth() or plot_vertical_depth ? Maybe evenplot_vertical_layer ? Just some initial thoughts.