ctrlc and updater

[RaitaroH]

A PR to merge the changes on develop:

• a function that tells when 'Ctrl-C' is pressed > adl can now more accurately count the number of episodes watched
• a function that let's adl update itself
  • [x] implement actual function
  • [x] implement -u / --update argument for it
  • [x] allow choosing what source: master (stable), or develop (unstable)
  • [x] update README.md accordingly

@Baitinq I will merge this tomorrow.