add option -e, -V; add pthread_join

Hey,

I made some changes to your code:
1.  Add a '-e' option, which allows me to specify file extensions like this:
 $ dirbuster-ng -e '.php,.zip,/,.html' -d ...
 (I guess you were meant to make it)
2. Add a '-V' option, which shows info for each request. This is useful for me sometimes, and I think it might be helpful for debugging.
3. Add pthread_join. Some weird error happens if we do not wait for the threads.

Any ideas??