Add a drupal filter support.

I've got a similar problem that can use the same solution. I've commonly run into sites that have people pasting the output of these word exports into the body field and getting a mess of things they didn't see on their export. Its not an actual part of their workflow to create this content in word, just a few people do so the base word2web module doesn't fit very well.

I've created a draft module(pretty complete) that shares code with word2web and creates a drupal filter. It is setup to be bundled with word2web currently as it seemed a more ideal solution. Attached is a patch that creates a shared include with the code for parsing/filtering out the word tags and provides the new word2web filter module.

I had to make a couple changes in the word2web filter to make it work better as a filter, abstract the code, and get around some utf8 problems I was having. I hope they are acceptable but I can split them out of if needed.