Feature: Emit audible/visible BELL signal when using a disabled function. (#86 and #87 by @clue)

By default, this project will emit an audible/visible BELL signal when the user tries to execute an otherwise disabled function, such as using the left or backspace keys when already at the beginning of the line.

Deprecated: Deprecate Readline class and move all methods to Stdio. (#84 by @clue)

// deprecated:
$stdio->getReadline()->setPrompt('> ');

// recommended alternative:
$stdio->setPrompt('> ');

Fix: Fix closing to emit final close event and clean up all listeners. (#88 by @clue)

Improve test suite to test against legacy PHP 5.3 through PHP 7.3 and support PHPUnit 7. (#85 by @clue)