Watch terminal size and react to resize events

[clue]

This project should watch the terminal size and emit an event when the terminal size changes. Among others, this helps with limiting user input (#4) and future mouse support (#82). If the size can not be determined, it should apply some sane defaults (most likely assume 80x24).

Refs https://softwareengineering.stackexchange.com/questions/148677/why-is-80-characters-the-standard-limit-for-code-width