Improve reliability

[tk3369]

Occasionally, the HoJBot would crash or stop functioning after a while. Until this known issue is fixed, I think we can still improve reliability but bouncing the bot often. Idea as follows:

1. Add a keyword argument to the start_bot function called duration_minutes;
2. Run an async task that
   • initialize a counter fromduration_minutes
   • wakes up every minute and count down
   • if counter becomes zero, exit the program
3. Modify the run.sh script to run the julia command in a loop.
4. Add a command line argument to run.sh to enable/disable the loop behavior. For example, I would disable the loop during development because I want to just hit Ctrl-C to exit. With this flag, it will never die.

[tk3369]

See #51 for an updated design