Logging to STDOUT

More information is taken during the watch process. Notably:
* How many total checks are made.
* The start/end time.

More verbose and user-friendly information printed to stdout. This includes:
* Printing a timestamp with each check.
* Catching and recovering from SIGINT.
* On program exit:
 * Print how many checks were made and the watch duration
 * The watching start and end time

Originally wanted to go further by recording statistics for each service/host and saving these logs to a file. I think a few other things need to be rewritten/expanded (notably HostWatcher) before this can be done properly. Merging this with master now so it doesn't get stale while I work on other issues.