Add optional Flash support for font list

Hello,

I've been playing around with your project after reading the EFF research paper.  The font list of a browser is a valuable source of entropy, so I decided to try and add it in.  I tried my best to make minimal API changes, and fail silently if the flash plugin fails, in order to continue on with the hashing process.

Thanks, and let me know if you'd like me to change anything in order to merge this pull request.

--Cal