Integration with vim-airline

[dnaaun]

First off, thank you for the great plugin!

I use this plugin regularly, and I keep finding myself wishing for a better indication of status. That's why I worked up a minimal implementation of an integration with vim-airline . All it does is show g:ipy_status on the status line.

If this sounds like a good idea, I've got some questions/suggestions:

1. I'm currently checking whether the current buffer's name is [jupyter]. It feels hacky to me, but I'm not an experienced vimmer.
2. If we had autocommands for when g:ipy_status changes, the status line can be updated ASAP, as opposed to whenever the status line is next refreshed.
3. Is there other things to show on the status line (apart from g:ipy_status)? For me, this in itself is sufficient.

I thought it might be better to post on this repo and get things cleared up before submitting a PR to vim-airline.