Bumped version to v2.4.0

Bumped version number to 2.3.0

Bumped version to v2.2.1

Tweaked annyang.removeCallback() documentation

Bumped version number to 2.1.0

[Added] New method annyang.isListening()

Updated version number to 2.0.0

Bumped to version 1.6.0

Updated devDependencies

Changed version to 1.4.0

Incremented to version v1.3.0