Updates and fixes for weather_pollen.pl

Fixes Issue #431.

While it would be possible to decode the forecast number from Pollen.com, it will require much more code and if they change the encryption scheme in the future (I've seen some accounts online where they have), the script will be broken again.  This pull changes the script to use Wunderground instead since their site is easier to parse and they actually get their pollen info from Pollen.com anyway.

I've also done some other general cleanup and made minor improvements to the script.