Add way to support multiple variables in dataset

[ahuang11]

#39

[jbusecke]

Hey @ahuang11, first of all many thanks for this awesome package! I just wowed people at the globally distributed km-scale-hackathon with this video:

https://www.youtube.com/watch?v=DwQJ-eYHQvc

I did have to use a hacky way (create a list of single time step datasets as iterative input, see this notebook ) to accomodate multiple variables. Having a simple way to pass datasets into the plotting function would be tremendous. Maybe something like:

stream(
     ...,
     var='all', # or var='dataset'
     ...
)

I could try to put in a PR if that is desired.

[ahuang11]

Hey apologies for the late reply, I was planning to take a look last weekend, but it slipped out of my mind 😢

However, if you're able to make a PR that'd be appreciated!