Add support for github

To-Do

- [x] Get data from GitHub after auth via curl statements.
- [x] Get all pages, in case of paginated data.
- [ ] Store all data into a single json file.
- [x] Make `sendmail` to mail the new notifications to user's email ID.
- [ ] Add a mailing template (`mail.txt.erb`), to be used with `sendmail` command utility to mail the new notifications.
- [ ] Add an easy `config.json` file rather than getting input from the program itself.
- [ ] Setup a bash script to automate this locally, which can be copy-pasted on `crontab`.
- [ ] Deploy cron job to server like Heroku.
- [ ] Properly `.gitignore` credentials.