the bot will now only post a reply if the comic selected is less than
12 hours old

The bot will now wait 60 seconds after sending a Tweet, to allow for the
API to recognize the most recent one. Also removed specific log
retention recommendation from README.md

Bug Fixes:
- Now checks the correct account for "in reply to"
- Correctly converts HTML to BeautifulSoup object
- Break HTML downloads when run successfully

Added dependencies to Pipfile. Created Twitter class (for API) and OAuth
header creation function.