Change the console.error to a opt in/out verbose mode.

[mikuhl-dev]

For example on https://github.com/ageitgey/node-unfluff/blob/master/src/stopwords.coffee#L16 I get this logged to my console on certain webpages, It's not necessarily a major error, so I would like to not see it fill up my console.

[mikuhl-dev]

Still having this problem.