#28 - strip out all alpha-numeric characters in default compaction strategy

Hey there, 

First off all, thanks for the awesome plugin.  As explained  in the issue, simply stripping out spaces doesn't seem to suffice for the latest versions of Chrome, Firefox, or Safari.  So, I made a change so that all non alphanumeric characters are stripped out in the default strategy.  if this works, we could apply the same love to other options as well.

LMK if this makes sense.

Best,
Shrisha