Let KeyboardInterrupt (Ctrl-C) end the break early

[sietse]

Hi Timothy,

Here is a more complete patch that

• ensures that concentration is always re-improved when a break ends, whether it ended naturally or because of a KeyboardInterrupt.
• updates the README.md to mention that Ctrl-C is supported
• updates the README.md to mention that Concentration works on Linux, Macintosh, and Windows.
• updates the ACKNOWLEDGE.md.

Thank you very much for creating Concentration, it is one of the first things I install when provisioning a new OS. The timed breaks are fantastic, and I really like the conversational style of commands like 'concentration improve' and 'concentration lose'.

Cheers, Sietse

[timothycrosley]

Sorry it took so long to merge this, but this is great work, thank you!