Replace tcell with roll-our-own

[walles]

• Fixes #37
• Fixes #34
• Makes window resizing smoother.

Before this change, the main loop was roughly:

• Await one single user input event
• Handle single user input event
• Redraw screen

With this change in place, the main loop is:

• Await one single user input event (like before)
• Handle single user input event (like before)
• If there are no more events, redraw screen (new!)

The difference is huge if you do a fling scroll on a trackpad. Before, scrolling was slow at constant speed, and the scrolling kept on at that slow constant speed way longer than what it should have. Now, scrolling feels just like it should.

[walles]

@89z could you test this on Windows?

If you could just build moar from this branch and try using it to view some file that would be swell!

You provided Windows screenshots in #33 so I assume you have a Windows machine with a Go environment set up.

[walles]

@89z thanks!

I excluded SIGWINCH handling on Windows, if you could make another try that would be awesome!

[walles]

Build + unit testing now pass on Windows, I added a Travis config so any breakage should become obvious.

Could still be visually all-broken though, needs testing by a human on an actual Windows machine.

Just starting moar on some file and verifying...

• Scroll down
• Quit

... should cover most Windows specific cases.

[walles]

I think it's because of this, no explicit access to /dev/stdout is ever done:

https://github.com/walles/moar/blob/7cd157174c028049ffa87c4b230a578c67a5481b/twin/screen.go#L105-L114

I'll see if I can figure out some way of testing this on Windows somehow.

[walles]

Found a Windows machine, will fix things up there.