add enchant.ActionEventTarget test
add enchant.Action test
add enchant.ParallelAction test
add enchant.Tween test
add enchant.Timeline test
add test case of enchant.Timeline
Merge branch 'feature/mocha_tl' into develop
bugfix about Action#dispatchEvent
use Easing.LINEAR as default
restore modification of a36ce99
modify Timeline#_activateTimeline test
bugfix about Timeline#next
modify Timeline#next to fix Timeline#que bug
modify Timeline#next test
remove unused variables in ParallelAction
refactor Timeline#waitUntil
add assertion to Timeline#then test
refactor Timeline#then
modify Timeline#tick
use Timeline#action