tty: implement binary I/O terminal mode

Introduce a uv_tty_mode_t enum for uv_tty_set_mode(), with backward
compatible values.  Add a new mode UV_TTY_MODE_IO, which uses
cfmakeraw() internally.

PR-URL: https://github.com/libuv/libuv/pull/86
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>