Make Lime color less sensitive

[jmsquare]

Hi,

I would like to make Lime colouring a bit less sensitive: highlight only words that have weights above a specific threshold.

None of the arguments of show_prediction enables to fix this threshold.

@kmike, @lopuhin @zzz4zzz. Is there a way?

A possible solution could be to add more opacity to the words where weights are not too large.