Updates

Finally got round to fixing a couple of issues with this project.
The program now does limit the number of concurrent threads used in checking for comic updates. The default limit is 8, but you can configure this in the comics.txt file. This was in the original design, I just forgot to implement it.
The other change is with displaying the comic. I am now using temporary files to cache comic pages. Previously the cache was stored in the RAM, which limits its size and sometimes caused Java to run out of memory.

There are also a few other minor tweaks and bug fixes.