Add pause feature

[caomem]

Another fun feature: now you can pause/continue the timer by press space.

I didn't split this PR with my last one about support datetime and new fonts.. in any case, it is so easy to split if needed (take a look in the properly commit). Sadly, I'm not sure if it works properly on windows (indeed, I don't think so; we need to use another library to give support to windows).

Have fun!

[1Blademaster]

@caomem I can't test it on windows today, but will try soon. Did you run this on linux or mac?

[caomem]

@1Blademaster I tested it on linux. I can test it on mac in few days, if needed, but I'm pretty sure that will works there.
I don't believe that it will works on windows because I'm using termios library, that is POSIX.. So this PR will broke in windows systems.
I can address this problem by check the system. But I can't test it on windows anyway. I will create a commit checking the system so you can test later, okay?

[caomem]

Done. With this last commit, the feature is ignored on windows systems, but can run on POSIX ones.

[caomem]

Hey! @1Blademaster please, don't merge it yet. I found a bug here: when I suspend the computer, the timer autopause.
I need to fix it.

[caomem]

Fixed. You can test :)