This commit is a major semver bump. Every progra utilizing escape codes generated by Termion is likely broken. The main change is to make each escape has their own type implementing the Display trait.

- Use formatters, mainly Display for escapes.

- Add Truecolor support (`color::Rgb`).

- Put each primitive into distinct modules.

- Add is_tty for checking if some stream is a TTY.

- Add multiple new examples.

The event system has been reworked to allow the detection of mouse
events as well as key presses.
Xterm, rxvt and X10 emulated escape codes are supported, they are
enabled and disabled by sending the right escape codes when creating a
RawTerminal.

To allow for byte manipulation, which was necessary to implement those
features, the backend iterator has been changed from chars() to bytes()
(with specific treatment of unicode sequences), making the whole crate
not require nightly rustc.

Fix example reference