Add aliases for options used for sets keyword

[zshaheen]

In addition to supporting sets = [3, 4, 5, 7], we can aliases for 3, 4, 5, and 7.

Maybe have:

• 3 == "zonal mean line"
• 4 == "zonal mean height contour"
• 5 == "lat long contour"
• 7 == "polar contour"

@chengzhuzhang, what are your thoughts and do you have ideas for keywords that are succinct?
I'll actually implement this, it's trivial.

[chengzhuzhang]

@zshaheen This, we can discuss with Chris and Jerry on Tuesday. I will have a list of possible names :)