prevent print_topics from truncating features

[alcantarar]

If printing features of varying lengths, especially when ngram > 1, print_topics output was difficult to interpret. Now adjusts topic width to fit longest feature in that topic.

[amueller]

Thanks for the PR. I'm not sure it's worth adding the feature, though. I'll probably get rid of mglean in the next major rewrite. It was never really meant as a practical tool, only as a companion for replicating figures from the book. With a bit of luck, the plotting functionality will be in sklearn "soon", or I might move to using yellowbrick or dabl for plotting.

[alcantarar]

No worries, seeing it in sklearn would be neat.

[amueller]

Feel free to open an issue there!